Of course it depends on how hard I rotate the bolt on the lug ramps correct?
Question about head space
So I bought a used shooter rifle supposedly built by Fulton in the 90s, has bedded std barrel in Mcmilian green stock, all GI parts. HR trigger win barrel Win bolt, etc. But I can tell it’s been used a lot, so I think this is a great rifle to tryout my new HS gages. I bought go, nogo and field. A range of.008 inches. I strip and clean the bolt. The nogo fully closes but no slop in the bolt, feels pretty tight. I’m hoping the field won’t close, but it closes about halfway down the lug ramp. I initially thought it was pretty stretched out but I read in one of the books that the axial movement of the bolt as the lug rides from the top of the ramp to the bottom is.006” so this means I’m .003 under field length HS , is that correct? I haven’t actually measured the axial movement along the lug ramps but it seems feasible. Thank you
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Do you have NATO gauges or SAAMI ?
Sounds like you are right in the ball park for a NATO spec chamber. If it doesn't close on the field, have fun.
You are using SAMMI spec 308W headspace gauges, and that reading is not uncommon with a 1960s era M14 barrel - as it has a NATO-spec chamber with corresponding headspace that is longer than the civilian/SAMMI spec chamber. I suspect your Field gage is 1.638” - and if it is almost closing - I would guess your headspace on that old USGI barrel is approx 1.636” or maybe 1.637”. That’s a typical M14 NATO spec chamber. I have a 1969 NM M14 barrel that headspaced at 1.636”, and my Navy M1 Garand with 1965 7.62mm barrel (aka Mk 2 Mod 1) also has the same 1.636” headspace. This makes sense once one understands that the “go” value is 1.6355” for 7.62x51mm in an M14. So they are relatively “tight” 7.62 NATO chambers - but “large” when compared to 308W SAMMI chambers.I’m hoping the field won’t close, but it closes about halfway down the lug ramp.
Very few people outside of specialized M14 gunsmiths have USGI 7.62x51mm NATO-spec M14 headspace gages, but here’s the difference re values:
SAMMI gages and values:
GO: 1.630 in.
NO-GO: 1.634 in.
FIELD: 1.638 in.
…versus.
7.62 NATO (M14 US MILSPEC) gage values.
GO: 1.6355 in.
NO-GO: 1.638 in.
FIELD: 1.6445 in.
Bottom-line: Your fired brass out of that M14 barrel will be slightly stretched and thus you’ll get less reloads (shorter brass life) if you re-size it back down to standard dimensions, but it should be safe to fire. The upside to that USGI barrel and it’s chrome-lined bore is that you will likely never burn it out…they will last a long, long time in a semi-auto rifle.
These are SAAMI gages by Forster. 1.630,1.634 and 1.638 thx
Wow I never looked at the NATO sizes. I knew they were longer, but I figured about.001 maybe.002. I am very surprised they are.0055 or.006 longer. That’s a big difference. Can you tell me something- does head space increase over time? I’m sure from new to maybe 50 or 100 rounds it compresses the seats a little, but does it basically stay the same for a while? It seems like chamber erosion increases it, but other than that, does it stay pretty constant for a while? Thx
I’ll defer to others re headspace change over time, but my understanding it’s more likely a subtle “bolt set-back” issue - rather than the chamber per se. Maybe old bolt action rifles not properly heat treated with high round count can have a “bolt set-back” issue? Again, no expert on this.
Others will know more, but I would not worry about it - esp with a chrome-lined barrel.
Others will know more, but I would not worry about it - esp with a chrome-lined barrel.
It will pretty much stay the same. No such thing as chamber erosion. There is throat erosion but most folks won't shoot enough to notice it.Wow I never looked at the NATO sizes. I knew they were longer, but I figured about.001 maybe.002. I am very surprised they are.0055 or.006 longer. That’s a big difference. Can you tell me something- does head space increase over time? I’m sure from new to maybe 50 or 100 rounds it compresses the seats a little, but does it basically stay the same for a while? It seems like chamber erosion increases it, but other than that, does it stay pretty constant for a while? Thx
If you close it on a NO-GO gauge and when you open it, it snaps open, then it's actually a little shorter than 1.636".
Here's the kicker-
The GO and NO-GO gauges are recommended ranges for a rifle WITH A NEW BARREL. Headspace will grow about 0.002" over the life of the barrel. So if it headspaces at 1.636" (NO-GO), then it will grow to 1.638" over the life of the barrel and reach the 308 Win FIELD REJECT length. From there, you're still 0.003" under NATO REBUILD MAXIMUM.
So, in short, if a rifle has long headspace, but is right at 308 WIN NO-GO, it's still safe to shoot for a while. I don't recommend reloading brass from a long chamber. It will fail sooner.
Tony.
Here's the kicker-
The GO and NO-GO gauges are recommended ranges for a rifle WITH A NEW BARREL. Headspace will grow about 0.002" over the life of the barrel. So if it headspaces at 1.636" (NO-GO), then it will grow to 1.638" over the life of the barrel and reach the 308 Win FIELD REJECT length. From there, you're still 0.003" under NATO REBUILD MAXIMUM.
So, in short, if a rifle has long headspace, but is right at 308 WIN NO-GO, it's still safe to shoot for a while. I don't recommend reloading brass from a long chamber. It will fail sooner.
Tony.
Just some more food for thought. When a USGI spec receiver,bolt,chrome tube are used the headspace will always be in the NATO range . Tightest one I have checked would be right at min 1.635 NATO min.
That's what they were designed to shoot .
All of my rifles are headspaced in this range because that's all I shoot Federal lake City and Winchester 7.62 NATO
Many USGI rifles will headspace 1.636- 1.638 average. When I build a M114 conversion and use a USGI chrome barrel they almost always end up at 1.637/1.638 because M1 locking lugs were .001 deeper plus most were well used.
Interestingly two of my latest projects using a post war SA M1 receiver in a conversion its lugs were at minimum depth which resulted in closer to min spec NATO range.
Most commercial parts builders tend to shoot for a tighter 1.632 - 1.633 headspace and that generally will comfortably shoot any NATO ammo .
Back when South African 7.62x51 was common I had an FA Armscorp build that was tight headspace 1.630 .It would not hand chamber these rounds as most cartridge headspace lengths were over the .308 GO by several thou.
That's what they were designed to shoot .
All of my rifles are headspaced in this range because that's all I shoot Federal lake City and Winchester 7.62 NATO
Many USGI rifles will headspace 1.636- 1.638 average. When I build a M114 conversion and use a USGI chrome barrel they almost always end up at 1.637/1.638 because M1 locking lugs were .001 deeper plus most were well used.
Interestingly two of my latest projects using a post war SA M1 receiver in a conversion its lugs were at minimum depth which resulted in closer to min spec NATO range.
Most commercial parts builders tend to shoot for a tighter 1.632 - 1.633 headspace and that generally will comfortably shoot any NATO ammo .
Back when South African 7.62x51 was common I had an FA Armscorp build that was tight headspace 1.630 .It would not hand chamber these rounds as most cartridge headspace lengths were over the .308 GO by several thou.
---------------------------------------------------...
The GO and NO-GO gauges are recommended ranges for a rifle WITH A NEW BARREL. Headspace will grow about 0.002" over the life of the barrel. ...
Yes, the GO & NO-GO gages are intended to be used when fitting a barrel.
Anyone have thoughts or knowledge about whether the chamber shoulder might 'compress' during use and result in HS growth. Or is the HS growth just in the bolt / receiver area?
My guess is there might be a tiny amount of 'shoulder compression', but most HS growth would be due to changes in the bolt / receiver.
Funny thing is , I have been building and shooting M1s and M14s for decades and monitoring headspace and throat erosion as they progress. Have not had one rifle out of dozens that showed any growth in headspace at all even after 8K on one of them. Been finishing barrels to a headspace of 1.632 - 1.633 and found that to be very reliable for accuracy with both .308 and NATO ammo. Throat erosion is another subject. That seems to happen faster using boat tailed bullets and slower with flat base. Been shooting between 5 and 10k per year of .308. I will put the headspace increase in the internet tales department. So many things we hear have no basis in real time fact other than read somewhere. An old time , reputable, M14 smith once told me that most of the headspace growth was total BS and could be credited directly to Forster gauges and improper use of the same causing wear and making them totally unreliable. He refused to use Forsters because they would never maintain calibration. I would venture to say that improper use of any make of gauge, that has not been checked for calibration should be considered as unreliable. Whatta Hobby!---------------------------------------------------
Yes, the GO & NO-GO gages are intended to be used when fitting a barrel.
Anyone have thoughts or knowledge about whether the chamber shoulder might 'compress' during use and result in HS growth. Or is the HS growth just in the bolt / receiver area?
My guess is there might be a tiny amount of 'shoulder compression', but most HS growth would be due to changes in the bolt / receiver.
Didn’t SAI in their 30k round test of an M1a find no change in headspace? Seems like if headspace shifted, that test would have shown some.Funny thing is , I have been building and shooting M1s and M14s for decades and monitoring headspace and throat erosion as they progress. Have not had one rifle out of dozens that showed any growth in headspace at all even after 8K on one of them. Been finishing barrels to a headspace of 1.632 - 1.633 and found that to be very reliable for accuracy with both .308 and NATO ammo. Throat erosion is another subject. That seems to happen faster using boat tailed bullets and slower with flat base. Been shooting between 5 and 10k per year of .308. I will put the headspace increase in the internet tales department. So many things we hear have no basis in real time fact other than read somewhere. An old time , reputable, M14 smith once told me that most of the headspace growth was total BS and could be credited directly to Forster gauges and improper use of the same causing wear and making them totally unreliable. He refused to use Forsters because they would never maintain calibration. I would venture to say that improper use of any make of gauge, that has not been checked for calibration should be considered as unreliable. Whatta Hobby!
That was what they said. Still some like to perpetuate rumors. Whatta Hobby!Didn’t SAI in their 30k round test of an M1a find no change in headspace? Seems like if headspace shifted, that test would have shown some.
My feeling is the reported “bolt set-back” issue is possibly limited to inappropriate caliber changes and the like, but I don’t think would ever apply to an M1 or M14 platform. It seems to be a bolt action issue with rifles that didn’t have a modern heat treatment processes, but have been “hot rodded” too much.
Here my understanding, converting a century old “small ring” Swedish Mauser (with century old heat treatment) into a barrel burning 300 Winchester Magnum - is possibly asking for a bolt-setback issue.
“Bolt lug set back is caused when cartridges that generate too much pressure and bolt thrust cause the bolt lugs to form indentations into the lug recesses in the receiver. The type of firearm that is usually most susceptible to this are small ring Mausers that have been converted to calibers that are too powerful for the action. It can also be caused by unsafe, heavy charges in handloads.
The symptoms of bolt lug setback are shiny depressions in the face of the lug recesses that are typically pushed back around .004" You need to remove the barrel to inspect this area of the receiver. Sometimes, if you gently pull back on the bolt handle as you close the bolt on an empty chamber you can feel the bolt lugs fall into these depressions.
Bolt lug set back causes excessive headspace in the weapon.
Here my understanding, converting a century old “small ring” Swedish Mauser (with century old heat treatment) into a barrel burning 300 Winchester Magnum - is possibly asking for a bolt-setback issue.
“Bolt lug set back is caused when cartridges that generate too much pressure and bolt thrust cause the bolt lugs to form indentations into the lug recesses in the receiver. The type of firearm that is usually most susceptible to this are small ring Mausers that have been converted to calibers that are too powerful for the action. It can also be caused by unsafe, heavy charges in handloads.
The symptoms of bolt lug setback are shiny depressions in the face of the lug recesses that are typically pushed back around .004" You need to remove the barrel to inspect this area of the receiver. Sometimes, if you gently pull back on the bolt handle as you close the bolt on an empty chamber you can feel the bolt lugs fall into these depressions.
Bolt lug set back causes excessive headspace in the weapon.
Only way headspace will change is poorly heat treated commercial receiver. USGI receivers just develope a mirror shine to the case layer .And if you look real hard you'll still see original machine marks.
To go from parkerized surface to mirror shine your talking maybe .001 .
I have a Winchester M1 receiver every contact point is mirror shine from who knows how many thousands of rounds fired to get that way .
If I install a new bolt and gage depth of face I find within a .001 of average gage length .
If your building a rifle a smooth lap to bolt and receiver lugs to remove park on lugs .Then set headspace off that you probably will never see a measurable change in headspace.
Now if you have a receiver on softer side especially one under spec. Yes I could see set back occurring.
One of the few problems with commercial receivers is heat treat. Most I have had were good in that respect.
Many USGI receivers are 58 - 60 HRC equivalent on surface.
To go from parkerized surface to mirror shine your talking maybe .001 .
I have a Winchester M1 receiver every contact point is mirror shine from who knows how many thousands of rounds fired to get that way .
If I install a new bolt and gage depth of face I find within a .001 of average gage length .
If your building a rifle a smooth lap to bolt and receiver lugs to remove park on lugs .Then set headspace off that you probably will never see a measurable change in headspace.
Now if you have a receiver on softer side especially one under spec. Yes I could see set back occurring.
One of the few problems with commercial receivers is heat treat. Most I have had were good in that respect.
Many USGI receivers are 58 - 60 HRC equivalent on surface.
Bolt set back I suspect occurs in the older bolt guns from too often firing from oiled chambers that increases the back thrust on the bolt face and of course the locking lugs. Also some military loads are hotter if they are loaded for a heavy machine gun.My feeling is the reported “bolt set-back” issue is possibly limited to inappropriate caliber changes and the like, but I don’t think would ever apply to an M1 or M14 platform. It seems to be a bolt action issue with rifles that didn’t have a modern heat treatment processes, but have been “hot rodded” too much.
Here my understanding, converting a century old “small ring” Swedish Mauser (with century old heat treatment) into a barrel burning 300 Winchester Magnum - is possibly asking for a bolt-setback issue.
“Bolt lug set back is caused when cartridges that generate too much pressure and bolt thrust cause the bolt lugs to form indentations into the lug recesses in the receiver. The type of firearm that is usually most susceptible to this are small ring Mausers that have been converted to calibers that are too powerful for the action. It can also be caused by unsafe, heavy charges in handloads.
The symptoms of bolt lug setback are shiny depressions in the face of the lug recesses that are typically pushed back around .004" You need to remove the barrel to inspect this area of the receiver. Sometimes, if you gently pull back on the bolt handle as you close the bolt on an empty chamber you can feel the bolt lugs fall into these depressions.
Bolt lug set back causes excessive headspace in the weapon.
My polytech that had a soft 40 rockwell bolt on gauges that I know were 308 was showing out of spec.
A field gauge that i think was intended for an M60 would not allow the bolt to close.
I put a TRW bolt in and the head space was to tight. My gunsmith checked the barrel and it was chromed. He said it should not be reamed. He ground the bolt face a bit with a special diamond tool and then it would chamber nato ammo a little bit tightly but read ok on the 308 gauge that he had. I decided for him not to grind more off of the TRW bolt.
For loaded nato ammo I push the edge of the shoulder back a hear with an old adjustable 30 cal seating die with seating stem backed out. Probably not kosher so to say but it works. I have not done anything with that rifle, but will go back to it soon.
For serious work I would use the looser polytech bolt for more reliable chambering. On the range it is the TRW bolt and suspect the trw bolt will never lose headspace, the soft polytech bolt will if it is used a lot. Some think that the chinese put a soft bolt in it on purpose. It was originally supplied to Muslim separatists in the Philippines is my understanding and who knows where those rifles will end up in the future or how relations will change.
faster powders like IMR 8208 will eat throats too if too many grains are added to the case. Unfortunately, my M1A likes the 8208 higher pressures for the best accuracy. I suspect my barrel life will be shorter than using H 4895 powder, which seems to be a little less accurate.Funny thing is , I have been building and shooting M1s and M14s for decades and monitoring headspace and throat erosion as they progress. Have not had one rifle out of dozens that showed any growth in headspace at all even after 8K on one of them. Been finishing barrels to a headspace of 1.632 - 1.633 and found that to be very reliable for accuracy with both .308 and NATO ammo. Throat erosion is another subject. That seems to happen faster using boat tailed bullets and slower with flat base. Been shooting between 5 and 10k per year of .308. I will put the headspace increase in the internet tales department. So many things we hear have no basis in real time fact other than read somewhere. An old time , reputable, M14 smith once told me that most of the headspace growth was total BS and could be credited directly to Forster gauges and improper use of the same causing wear and making them totally unreliable. He refused to use Forsters because they would never maintain calibration. I would venture to say that improper use of any make of gauge, that has not been checked for calibration should be considered as unreliable. Whatta Hobby!
Thanks for all the responses. I have a small collection of pre-ban mainly (GI Parts) rifles, so I won't shoot any one of them alot of rounds. I was a little concerned about the older GI rifle headspacing at halway down the Field ramp, with a Forsner gage for what thats worth. So I'd like to think I'm 1.636 but I might be 1.637. So I'm .001 under field length (for SAMI). Again since I wont be shooting it often I'm not worried. I just want to know I can shoot the first round and not get a face full of blast. (I always turn my head away when I shoot a new rifle first round). Thanks again
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