[Shortbox4x4]

Throat design does help accuracy and or hurt it. It’s not just the freebore length but the freebore diameter as well as the angle lead in. Some chambers throats don’t even have a straight/parallel section of the freebore. The throat just starts out as a funnel back at the case mouth. This does nothing to help bullet alignment when making the jump from the case and into the rifling. The SAAMI 300win mag is a absolute horrible design is a good example. At the case mouth it starts out at .317” diameter but the just tapers in like a funnel.

The 308w case capacity is almost the perfect case volume for bore size in 30cal. It’s the most efficient. This makes the 308w also more forgiving in terms of ignition. Typically the fuller the case is with powder the more uniform the burn vs having a case with an air pocket in it per say.

The 30-06 is just as an accurate as a cartridge as the 308w is. The 308w if you will if you want to say it a different way Is more consistent. This goes back to the burn of the powder.

There are differences between the 308w SAAMI, 7.62 NATO and even the 7.62 NATO NM chamber. Of those three the 308w SAAMI is a better design.

Also the 7.62nato chambers if I remember correctly (I don’t have the drawings in front of me as I’m not at work) but the case body of the chamber is also looser/bigger than 308w SAAMI.

Besides the above chamber spec’s we have three different 308 chamber designs we use at work on building custom rifles. The only thing different is in the throat design. Which we use depending on the ammo/bullets the customer will be shooting. One reamer with a short throat which is the 308w Obermeyer reamer. This is for 175gr and lighter bullets. It will also chamber most box ammo. Then we have a med. throat reamer which is +.020” longer than the Obermeyer. Then we have a really long throated reamer just for shooting 200gr or heavier bullets for like a FTR gun.

30-06…we have the SAAMI min spec. Which unless it’s called for in ammunition test barrels where it has to be SAAMI spec.I don’t use it for custom builds on bolt guns. We have the Serengti reamer but I wouldn’t use this if the customer is going to shoot box ammo as I feel the throat is too short/tight. Strictly a bolt gun match chamber. Then I have another reamer which I call the 30-06HVT. I designed the throat of this reamer based on factory 30-06 M72 box ammo. I tried to find the longest loaded round and measured it from the base of the cartridge to the ogive of the bullet and then added another .020” to the freebore length and made a straight parallel section with a freebore diameter of .3085” I think it is. With a 1 degree 30 min lead angle.

The one M1G barrel I did in a service rifle pattern when I rebarreled one of my Garands has that one reamer.

So back to the main question. Is a 308w more accurate than a 30-06? With standard chamber and loads…I’ll give the tip to 308w but not necessarily more accurate but more consistent. The 30-06 with the right density load of powder and a decent designed throat…I don’t think the 308w has anything on it.

I have two bolt guns built (one set up as a K98 sniper type resto mod gun) and another gun I used for testing back when we started Krieger. So it’s a single shot rifle I used for accuracy testing. Both of these guns have a chamber that I call 7.5HVT. It’s a 8mm Mauser case necked down to 30cal. Back in the 1930’s the French actually where playing around with the caliber and might have used it just for a short bit. I’d have to look at my notes but I think it was called 7.5x58mm. Has a tad more case capacity than a 308w but less than a 30-06. I designed my own throat for it. It is very accurate and easy to load for. The only down side is it won’t run thru a short action bolt gun.

Later, Frank

PS if your wondering what the HVT stands for…I call it high velocity target. Even though the caliber might not be a really high velocity round. The first round I gave this name to was 12.7x114mm chamber. I rebarreled a dewat Lahti to 50cal but instead of doing 50bmg as the rim is smaller than the 20x138B Solothurn round I took 14.5x114 Russian cases and necked it down to 50cal. The rounds fed out of the Lahti mags and I didn’t have to rework the bolt face or modify the extractor as the the 14.5 and the 20mm used the same case rim diameter. My everyday working load for that gun slung a 750gr AMAX bullet at 3100fps and I wasn’t stepping on it/beating up the gun.

 

[Shortbox4x4]

Frank- thanks for the thoughtful response. I think your comments/experience align with my belief about a good chamber bringing excellent accuracy to 30-06. The chamber you describe sounds like a good one (30-06HVT). That would be fun to try out in a M1903 USMC sniper clone too. I have not put a new 30-06 barrel on a Garand or 1903 in a while, but those used the SAAMI reamer. They shoot well for what they are, but next time it will be something better like the HVT. I also think my rechambering plan might have merit when the 308 throat is smoked....unless of course you start making some M1 Garand heavies..

I used that reamer in the 03 that I rebuilt also.

M1G heavies. Might make a run of them. Only have 3 guys at this time showing interests at this time in a hvy pattern and 3 interested in a service rifle pattern. If you are interested in one send me your email address and name along with a phone number. When I have pricing figured out I’ll notify everyone on the list.

The hvy pattern at this time will be S.S. only. All of the 30cal barrels for M14’s also will have 5R rifling and 1-11 twist at this time.

 

[Shortbox4x4]

It is a common myth that the M14, M60, M240, etc chambers are larger, looser, bigger than SAAMI spec chambers.

Here is an overlay of several "NATO" chambers, as you can see the diametrical difference between the bodies is 0.0007 to 0.0013. The headspace difference is around 0.010, with the MG chambers noticeably shorter.

View attachment 498313

View attachment 498314

View attachment 498315

Like I said I was going off of memory and I need the drawings in front of me. If I recall correctly the throat diameter on the 7.62 NATO is .316” and the 308w SAAMI is .310”. I don’t recall freebore length on those.

I can post the drawings on Monday. I have them all saved on my computer at work.

 

[Shortbox4x4]

It is a common myth that the M14, M60, M240, etc chambers are larger, looser, bigger than SAAMI spec chambers.

Here is an overlay of several "NATO" chambers, as you can see the diametrical difference between the bodies is 0.0007 to 0.0013. The headspace difference is around 0.010, with the MG chambers noticeably shorter.

On the headspace difference of around .010” are you talking about go +.010“ if using a field gauge vs saami on 308w being go +.006” typically being max.?

I know on the drawing I have for 7.62 nato it shows a min. dimension of 1.628” which is .002” shorter than a 308w min of 1.630”.

I didn’t know the MG chambers could be even shorter? Any idea as to why?

 

[Shortbox4x4]

Some how I blocked out part of the post…but my question is pertaining to the headspace length difference. I ended up adding it to part of your post and taking out the drawing. Sorry…don’t know how to undo it.

 

[Shortbox4x4]

Well that cracks me up and not surprising.

If for example the 7.62 nato spec reamer is suppose to be a standard you think that would be the standard used in guns?

I’ve seen the same thing if you will in production guns (commercial) there is the saami min spec standard but that doesn’t mean a manufacturer uses that standard.

This is a good reason why whenever someone orders test barrels from us and don’t supply a print for everything and just call out 300wm or any other caliber/chamber I reference the tool part number on the drawing and put that info on the sales order confirmation copy so there is a track record of what we made the barrels to. They get all that info sent to them in the confirmation for review. That way it cannot come back on us making the barrels wrong.

I’m dealing with this headache right now with an overseas customers for finished M40 sniper rifle barrels for they’re military. The order is for two batches of 350. They’re prints don’t show enough detail when it comes to the chamber. They call it 7.62x51mm. So I’ve sent them several different prints for them to tell me which reamer to use and no one at the arsenal (can’t talk to anyone directly as is has to go thru a contractor which no one there knows anything about guns) can tell me which exact chamber spec it is!

So I’m hesitant on taking the job as they have a accuracy requirement at 200 yards the barrel has to meet. They say they are using three different types of ammo which are 308w Federal GMM with a 175gr bullet, M80 ball, and a 3rd some foreign 308 match round which escapes me right now.

So they ordered two barrels for testing. One with the 7.62 nato reamer and one with the 308w SAAMI reamer.

I’ve also asked how are they inspecting the chambers and bores so we do apples and apples for inspection. No one gets back to me. That’s why I’m hesitant on taking the job. Poor communication and I don’t want anything coming back at us.

 

[Shortbox4x4]

Yes, that is a big problem when non-technical people get stuck dealing with technical issues. I'll bet your foreign customers don't even have engineering support to answer your questions.

If it helps, the USMC M40A3 barrel drawing specifies the chamber dimensions shall conform to AMSI/SAAMI Z299.4, .308 Winchester.

You are correct…it’s a big problem. Every question I ask has to go thru the contracting people if you will and they have to relay it to the Arsenal. I’ve begged and pleaded to be able to talk to someone directly at the Arsenal to no avail! Everything had to get relayed!

I’ve got the whole M40A3 rifle build drawings. It includes everything even the scope mounts etc…I’ve even made references to what some of our military uses in they’re sniper rifles being 308w SAAMI. Falls on deaf ears.

I’ve been in similar situations with our gov’t and an ammo maker when it came to the 300wm sniper ammo. What was funny about that was the contracting officer in charge which was a woman at the time (about 5 years ago this happened) actually figured out they had a ammo spec problem. When she made reference in saying that on a conference call…one of the military guys blew a gasket on her and told her to be quiet that they didn’t have a ammo problem. You just can’t make it up.

2 years ago I got an order for some 9mm test barrels for a ammunition maker. So when I was looking at the prints closely I noticed the bore and groove spec’s where not SAAMI and they also where not Nato. It was a hybrid of both. Then I looked at the chamber…again it wasn’t SAAMI and it wasn’t Nato. So I asked the ammo maker…do you have the chamber reamer? Because we don’t! They said no. Could I order one and at it to the bill? I said it was proprietary and the reamer maker couldn’t make it for us. Luckily I looked in the small detail of the print title block and I figured out who the manufacturer of the gun was. I had contacts at that manufacturer because we make precision barrels for them as well as R&D barrels for them. So I got a hold of the guy I talk to all the time there even though he deals with rifles only and could he put me in contact with whom ever is in charge of the handgun stuff. Bingo…got the chamber prints released to me in detail and they gave the ok to the reamer maker to make us the chamber tools.

It works out sometimes and sometimes….it is just a cluster!