Help with high pressure loads.

[cosmic]

Well - Lets see, short freebore giving diminished case volume, possible tight bore, loads approaching book max. All the necessary ingredients for high pressures. Yes - your rifle is pressure prone.
You need to back off on the charge weight for this powder, and avoid going near book max with any other powder.

 

[bigedp51]

Two of the rounds were jammed in the chamber (one was really bad and took a second person to help motar it out). I checked these in a chamber gauge and the headstano on these two rounds were about 1/8th below the acceptable range.

I ran a few rounds of 168 gr hornady Tap factory ammo and got the same results - 2 rounds had some pressure signs and 3 had blown out primers.

What I do not understand is how a fired case can be 1/8 of an inch below your Wilson gauge and be considered over pressure.

Meaning the chamber pressure should have forced the case against the bolt face and been a snug fit in headspace length.

Plus the only way I know of to make a case that short in a case gauge is for the bottom of the sizing die to be ground down or using a Whidden sizing die. Meaning the case shoulders were setback too far during sizing.

 

[Luis1]

What I do not understand is how a fired case can be 1/8 of an inch below your Wilson gauge and be considered over pressure.

Meaning the chamber pressure should have forced the case against the bolt face and been a snug fit in headspace length.

Plus the only way I know of to make a case that short in a case gauge is for the bottom of the sizing die to be ground down or using a Whidden sizing die. Meaning the case shoulders were setback too far during sizing.

I agree. I will clarify because I missed information. These rounds were properly sized before loading and firing. Both of these happened during firing the ladder. Never at the beginning of the ladder. The were both hard to get out after and were not fired. I will add a pic of the case in a bit and you will see what I mean.

So this shortening of the case occurred during the loading sequence of the action.

 

[209jones]

Is there something about the OAL or the case sizing that is preventing the bolt from achieving full lockup? Autoloaders don't have the camming power to overcome case and OAL issues the way a bolt or break or lever does. You didn't say what the datum line to the shoulder length after firing was vs the sized length as far as I can see. Were those cases FLS"d or partial sized, were they fired in that gun before sizing? Some of the info doesn't really add up.

 

[Ganderite]

I have a number of "identical" rifles. I often build rifles 3 at a time (3 of us in the family are shooters) Using custom barrels, chambered with my own reamer, each rifle turns out to be different. The cambers are so similar the fired cases will chamber in all 3 rifles, but the velocity difference can be 150 fps higher in one rifle.

It sounds to me that you have a "fast" rifle. Start low and develop your best load.

And if you ever blow a primer - STOP SHOOTING. I recall a fellow who didn't, and on the third or 4th shot, the rifle blew. God gave him warnings that he ignored.

 

[Ltbull01]

2700 fps out of a 18" barrel with 168 would in my opinion be running at pretty high pressure. Even if the load is within book data, it can still have excessive pressure. A change in brass or any other component, a new powder lot, can all give high pressure to what is an otherwise safe load.

 

[OldDude]

Have you tried a similar load development cycle with a different brand of brass? I've had Hornady factory rounds that left extractor marks on about 1/3 of the cases in a box.....

 

[Luis1]

Is there something about the OAL or the case sizing that is preventing the bolt from achieving full lockup? Autoloaders don't have the camming power to overcome case and OAL issues the way a bolt or break or lever does. You didn't say what the datum line to the shoulder length after firing was vs the sized length as far as I can see. Were those cases FLS"d or partial sized, were they fired in that gun before sizing? Some of the info doesn't really add up.

209jones - I honestly don't know what the datum line is after sizing. The cases were full length sized before firing, and the brass either purchased by me or shot prior out of a buddies rifle from factory loads (which he gave me afterwords) . I only use range brass for link pressure plinking loads, never for these type. The cases are trimmed to 2.002 - 2.004 (tolerance variation).

Here are pictures of one of those two rounds that got "pushed" (I'm assuming farther into the chamber.

 

[Luis1]

2700 fps out of a 18" barrel with 168 would in my opinion be running at pretty high pressure. Even if the load is within book data, it can still have excessive pressure. A change in brass or any other component, a new powder lot, can all give high pressure to what is an otherwise safe load.

I think that may have been part of the issue. I do now recall using winchester brass for my initial ladder with this load. And I agree 2700 is very fast for this barrel length. I will be scrapping this ladder and restarting from scratch.

 

[Luis1]

Have you tried a similar load development cycle with a different brand of brass? I've had Hornady factory rounds that left extractor marks on about 1/3 of the cases in a box.....

Yea the initial ladder with this load/powder was with winchester brass.. I think this is stupid me for changing brass at this point.

 

[Luis1]

I have a number of "identical" rifles. I often build rifles 3 at a time (3 of us in the family are shooters) Using custom barrels, chambered with my own reamer, each rifle turns out to be different. The cambers are so similar the fired cases will chamber in all 3 rifles, but the velocity difference can be 150 fps higher in one rifle.

It sounds to me that you have a "fast" rifle. Start low and develop your best load.

And if you ever blow a primer - STOP SHOOTING. I recall a fellow who didn't, and on the third or 4th shot, the rifle blew. God gave him warnings that he ignored.

I will be doing that for sure. And I do agree it was stupid of me to fire an additional few rounds. It could have led to disaster or worse.

 

[Luis1]

Here is additional pic of the picture above. On the left is the case with the shorter shoulder after it was extracted. The right is a fresh case that has been resized and is ready to load. You can see the one on the left has a shorter shoulder than the one on the right.

 

[cosmic]

Well - That's really weird! The only possible thing that I can think of is that you were sizing the cases incorrectly at some point. The case on the left shows soot marks on the case - possibly indicative of a grossly undersized case. If the cases are undersized then you can have problems comparable to excessive headspace in the rifle.
Alternatively, the case on the right may have had the neck and shoulders "pulled" due to lack of lube inside the case neck. Will this case chamber in your rifle?

 

[bigedp51]

Question?

Have you been shooting this rifle with a silencer/suppressor? This can carbon up the chamber very quickly and gum up the works.

I think you stated the case on the right was not fired but you have carbon sticking to the sides of the case. Meaning the chamber is full of carbon that makes me want to ask when you cleaned the chamber and throat of your rifle last. And high pressure can be caused by a carbon ring in the neck of the chamber, preventing the neck from expanding.

Also in a semi-auto the resized case body should be .003 to .005 smaller in diameter than its fired diameter. This allows the case to spring back from the camber walls and extract reliably. And you have carbon sticking to the case body just below the case shoulder and some lower down. Meaning the case on the left in your photo has a case body that was dragging on the chamber walls and may be too large in diameter.

Were these cases range pickup brass or fired in another rifle or sized by someone else?

Below M14-M1A load data.

.308 Match Loads Effective out to 200 and 300 Meters
The primary (accuracy) powder charge for each load is noted below. A range of powder grains is included for load tweaking purposes.
168 gr. SMK, 39.0 gr. (37.0 to 39.0 gr.) IMR 3031, LC Match, Fed 210 Primer
168 gr. SMK, 39.0 gr. (38.5 to 40.5 gr.) IMR 4895, LC Match, Fed 210 Primer
168 gr. SMK, 40.5 gr. (38.5 to 40.5 gr.) IMR 4895, LC Match, Fed 210 Primer
168 gr. SMK, 40.0 gr. (38.0 to 40.0 gr.) H-4895, LC Match, Fed 210 Primer
168 gr. SMK, 40.0 gr. (39.5 to 41.5 gr.) IMR 4064, LC Match, Fed 210 Primer
168 gr. SMK, 43.0 gr. (41.0 to 43.0 gr.) Win 748, LC Match, Fed 210 Primer

NRA 7.62x51mm Lake City load data for M1-A's.

https://www.ar15.com/forums/armory/NRA_7_62x51mm_Lake_City_load_data_for_M1_A_s_/42-441371/?

 

[OldDude]

Yea the initial ladder with this load/powder was with winchester brass.. I think this is stupid me for changing brass at this point.

Have you compared the weights of the Hornady vs. Winchester brass? This would rule out case thickness variations or brass hardness variations.

BTW, the Hornady factory rounds I mentioned earlier with the extractor marks came out of rifles which had no such marks using other brands of factory ammo. I'm wondering if the Hornady brass has a softer head.....

 

[Luis1]

Well - That's really weird! The only possible thing that I can think of is that you were sizing the cases incorrectly at some point. The case on the left shows soot marks on the case - possibly indicative of a grossly undersized case. If the cases are undersized then you can have problems comparable to excessive headspace in the rifle.
Alternatively, the case on the right may have had the neck and shoulders "pulled" due to lack of lube inside the case neck. Will this case chamber in your rifle?

Yea there was more than enough case lube on the inside and outside of the cases and case necks. The picture for some reason came out a bit scewed. The right case does not. Look "lop sided" in real life. The case on the left was undersized coming out of the rifle. It was properly sized before firing, or attempt to being fired.

 

[Luis1]

Question?

Have you been shooting this rifle with a silencer/suppressor? This can carbon up the chamber very quickly and gum up the works.

I think you stated the case on the right was not fired but you have carbon sticking to the sides of the case. Meaning the chamber is full of carbon that makes me want to ask when you cleaned the chamber and throat of your rifle last. And high pressure can be caused by a carbon ring in the neck of the chamber, preventing the neck from expanding.

Also in a semi-auto the resized case body should be .003 to .005 smaller in diameter than its fired diameter. This allows the case to spring back from the camber walls and extract reliably. And you have carbon sticking to the case body just below the case shoulder and some lower down. Meaning the case on the left in your photo has a case body that was dragging on the chamber walls and may be too large in diameter.

Were these cases range pickup brass or fired in another rifle or sized by someone else?

Below M14-M1A load data.

.308 Match Loads Effective out to 200 and 300 Meters
The primary (accuracy) powder charge for each load is noted below. A range of powder grains is included for load tweaking purposes.
168 gr. SMK, 39.0 gr. (37.0 to 39.0 gr.) IMR 3031, LC Match, Fed 210 Primer
168 gr. SMK, 39.0 gr. (38.5 to 40.5 gr.) IMR 4895, LC Match, Fed 210 Primer
168 gr. SMK, 40.5 gr. (38.5 to 40.5 gr.) IMR 4895, LC Match, Fed 210 Primer
168 gr. SMK, 40.0 gr. (38.0 to 40.0 gr.) H-4895, LC Match, Fed 210 Primer
168 gr. SMK, 40.0 gr. (39.5 to 41.5 gr.) IMR 4064, LC Match, Fed 210 Primer
168 gr. SMK, 43.0 gr. (41.0 to 43.0 gr.) Win 748, LC Match, Fed 210 Primer

NRA 7.62x51mm Lake City load data for M1-A's.

https://www.ar15.com/forums/armory/NRA_7_62x51mm_Lake_City_load_data_for_M1_A_s_/42-441371/?

No lol... No suppressors here in this country... With all of its stupid laws and stupid politicians like Tru-dumb-#### here... Lol.

I think maybe 70 rounds or so since last cleaning... Not much. The last very thorough cleaning was several hundred rounds ago and before that when I first got the rifle.

I will do a very thorough cleaning this weekend and take it out again. Thanks for the load data I will look at those and maybe base some of my loads on that data. Now answer me this should I be using a small based sizing die with this round for this rifle?

 

[bigedp51]

No lol... No suppressors here in this country... With all of its stupid laws and stupid politicians like Tru-dumb-#### here... Lol.

I think maybe 70 rounds or so since last cleaning... Not much. The last very thorough cleaning was several hundred rounds ago and before that when I first got the rifle.

I will do a very thorough cleaning this weekend and take it out again. Thanks for the load data I will look at those and maybe base some of my loads on that data. Now answer me this should I be using a small based sizing die with this round for this rifle?

Are your resized cases .003 to .005 smaller in diameter than their fired diameter?

The answer to your question depends on the diameter of your chamber and most semi-auto and pump actions have a chamber on the large size.

Bottom line measure your case body at three points after firing and after sizing.

 

[Luis1]

Ok thanks I will do that and get back to you with the results

 

[just having some fun]

Here is additional pic of the picture above. On the left is the case with the shorter shoulder after it was extracted. The right is a fresh case that has been resized and is ready to load. You can see the one on the left has a shorter shoulder than the one on the right.

Not a expert on the stag 10 but by the look of your brass...

I have a M305 and once fired 400 rounds with out cleaning it .. cleaned it after getting rained on..

My Brass after those 400 rounds looked so much better than your brass

i would only toss it in the vibratory tumbler for 15 min and it would come out looking brand new .... then size it