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M1A Scout over pressure at "normal" load

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There are lots of old posts about the right load for an M1A Scout 18" barrel. I had been using 43gr IMR4895 under 168gr HPBT from Hornady with Winchester LPR primers. My brass is mixed - hornady, winchester, lc (with reamed pockets), PMC. What concerns me are the flattened primers. Isn't this showing over pressurization? I worked up some other test loads and was still flattening primers down to 38gr in half grain increments. I tried a Federal 7.62 NATO round and it does NOT flatten the primer. Should I just ignore the flattened primers?
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if your going to do any load research,you need a good chronograph to see what the fps of each load is.
 

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that might be a bit stout as I use 42.0gr H4895 under 125/175gr bullets and mild flattening?


Any pics of your primers will help the crowd here reply
 

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I worked up some other test loads and was still flattening primers down to 38gr in half grain increments.
"Flattened" primers sometimes occur due to oversized/overworked brass. The shoulder possibly was bumped too far, causing a "gap" between the boltface and primer. The primer initially backs out upon firing then gets flattened as the case expands.
 

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First, you have to understand that a primer flattened by overpressure will fill the groove that surrounds the primer. If you still have a groove around the primer, you're fine.

Second, Federal uses 43 grains under a 168 in their Gold Medal and OTM loads. In a commercial case, that is fine. In a LC case, lower it to 42.5 grains.

Third, and most important, don't be shoving a 168 down to the 2.80 OAL. Your magazine will hold cartridges out to 2.820, take advantage of it.

The middle case below is often mistaken for a flattened primer, but the groove is still present. The case on the right has a primer that is flattened by over pressure.
 

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Seat for pressure and barrel time, you will never hit the lands in an M1a. Barrel time is one of the most important factors in a charge, other than burn rate. 16 socom barrel time of .896 Ms is about perfect.
 

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Would the barrel length make a big difference? I would guess that the max pressure in the case would occur before the bullet got that far down the barrel
Barrel length effects port pressure, not chamber pressure. Throat length can effect chamber pressure, but as stated above, your bullet will never touch the lands of an M14 barrel.
 

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First, you have to understand that a primer flattened by overpressure will fill the groove that surrounds the primer. If you still have a groove around the primer, you're fine.

Second, Federal uses 43 grains under a 168 in their Gold Medal and OTM loads. In a commercial case, that is fine. In a LC case, lower it to 42.5 grains.

Third, and most important, don't be shoving a 168 down to the 2.80 OAL. Your magazine will hold cartridges out to 2.820, take advantage of it.

The middle case below is often mistaken for a flattened primer, but the groove is still present. The case on the right has a primer that is flattened by over pressure.
I thought 4064 was used in the FGMM load. I would consider 43 grs of 4895 on the warm side.
 

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My understanding is that 'primer flattening' happens this way -

1) On initial ignition of the powder (or maybe just the primer itself) the primer gets moved out of the case slightly.

2) Further ignition of the powder causes high pressure inside the case and forces the base of the case rearward against the bolt face and 'reseats' the primer.

3) If the primer pocket is somewhat loose (e.g. with reloads, versus new factory ammo), the action in #1 can be more violent and cause the primer OD to increase before #2 happens.

I think the earlier advice about observing the amount of flattening is good to judge between OK and over-pressure.

Unless you are using that 43gr load for distances beyond 300 yards, I think you'd be better off reducing to about 41 grains - especially when 'mixed brass' is used. 41 grains should give good accuracy, and will be less wearing on the rifle and cases.

Jay
 

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I thought 4064 was used in the FGMM load. I would consider 43 grs of 4895 on the warm side.
you wont really know what powder is in the factory loads. They buy it in large bulk that gives them the what they are looking for in results burn rate and pressure

If you have any factory ammo that spreads out in a few lot#s break some down from each lot. Most likely you will find different powders and charge weights.

I emailed creedmoor to see what they used for powder in their 30-06 match loads and they stated each batch they buy is different and loads are worked up for each new lot. Our powder is not the same as commercial offerings.
Linked me to a review with some photos. Scroll down
http://bulletin.accurateshooter.com/2017/10/excellent-factory-ammo-offered-by-creedmoor-sports/

Im going to gander Federal uses what ever bulk powder that fits their needs at the time they order it. I have 1 round of federal 175 grain match. maybe I will break it down?
 

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There are lots of old posts about the right load for an M1A Scout 18" barrel. I had been using 43gr IMR4895 under 168gr HPBT from Hornady with Winchester LPR primers. My brass is mixed - hornady, winchester, lc (with reamed pockets), PMC. What concerns me are the flattened primers. Isn't this showing over pressurization? I worked up some other test loads and was still flattening primers down to 38gr in half grain increments. I tried a Federal 7.62 NATO round and it does NOT flatten the primer. Should I just ignore the flattened primers?
43 grains of IMR 4895 is 1.5 grains OVER maximum in the Sierra book. I would drop that load by at least 2 grains and start over.

I have no doubts that you are well over pressure.
 

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I thought 4064 was used in the FGMM load. I would consider 43 grs of 4895 on the warm side.
43 grains of 4064 is reported to be one of the 'recipes' Federal has used.

43 grains of IMR 4895 in a case as heavy as FC is asking for trouble.
 
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