Winchester 748 issues

Originally Posted By: 6724Originally Posted By: cjclemensOk, so I weighed the charges from the pulled loads. The leftovers consisted of one from each charge I used. The ones I weighed happened to be my minimum and maximum charges - 26.6 grains and 27.5 grains respectively. That means the ones that popped primers were 26.9 and 27.2 grains. Max charge for a 50 grain projectile in the Hornady book I used is 28.3, but the varmint grenades are a much longer bullet, so I tried to stay well under max. Maybe this was more compressed than I thought - but that still doesn’t explain why I didn’t see pressure signs the first time.

I’m not afraid to pop a primer or two, as long as that’s my worst mistake. I just prefer to learn something from it so I don’t do it again. That’s also why I posted it in here. If I did something stupid, I expect y’all to call me out on it.

Just because the book says that is max, that doesn't mean squat. Your rifle versus the test rifle could be different in many respects, how tight is the chamber, how much freebore, what brass, what seating depth, and on and on.
I have been using 748 for nearly 30 years, I have never had a primer blow out on an AR15. In fact, I have never blown a primer except with an AR10 that was way over gassed. The load was not high, but the bolt was opening under pressure leaving an unsupported case head. Off the top of my head, 27gr seems like a very stiff load. I have never compressed the powder with 748.

Sounds to me like a simple case of too much powder stuffed in the case.

Maybe so, but that doesn't really explain why I didn't see pressure signs the first time I shot the same loads.
 
CJ,

Did you check the overall length of the brass? By chance?

If forgot to trim brass one time for my Colt Carbine 6920. I ran a ***** hot load of 2520 with 70 grain Barnes TSX bullets.. The brass of the same batch that "were ready to load" but not loaded averaged 1.764

Ironically nothing happened. No pressure. I guess hogged out Colt 5.56 chambers go way further.

I got lucky on that one i think. 2850 fps out of a 16 inch barrel is to fast. It was LC brass though.

I have been so busy preparing the addition onto my house for the next kid, that i have not shot a rifle in months.

All my loads of W748 were made this winter in 30 - 50 degree weather. I use 26.8 grains for Sierra #1390's (55 grain HP's) without problems. That 6724 of mine has the longest throat out of all the rifles i have. Yet still shoots the tiniest groups i have ever seen.


I think the moral of this story is that you were over the fence last time. Just using tough brass that covered the symptoms. An increase in temperature, a dirty barrel and letting the round warm up or a combination there of took it to the next level.

It is hard to know with tough components sometimes if you are seeing pressure or not. The best way to find out is to take the fired rounds home and reload them again. If the primer pockets are loose you are to hot. That coupled of course with some chronograph readings gives a baseline .

Though in my past experience, i have flattened a lot of CCI 400's before seeing brass stress.

Its a fun/tougher game loading up bullets that have no data or base line for the powder type you are trying to use.
 
cj, I have shot untold thousands of 27.5g of 748 with a 7 1/2, 50g Sierra blitz. Load for the 55g was 26.5g, with same primer. Rem, Fed, Win, IMI brass.

Ammo that has got sitting in the sun will add to pressure, hot chamber will add to pressure, 9T vs a 14T will add to the pressure a tad bit.

The long bearing surface of that bullet I think is what got you into trouble, and the thin cup primer is not help. Blown primers are a function of loose primer pockets to begin with, and high pressures on the load..thick cup primers would have nothing to do with this issue.

I am not sure what Lake city brass would do for your loads in terms of increasing pressure.

All of my shooting was done in bolt guns, and I did get the barrels screaming hot on dog towns.

Federal brass is pure crap with soft case heads, you will loose the primer pockets fast.
 
Just the other day I loaded up some very long 70 grain bullets for the AR. I seated them to mag length with a load of 24 gr of Varget. Not a max load by a grain or so. Blew the primers right out of the brass. These were CCI 450's. Anyhow, point is I had a brain fart and forgot that if I use up the space in the cartridge seating the bullet deep I increase the chamber pressure. Duh! Had to pull 250 projectiles and replace them with appropriate projectiles for mag length loads.
 
Our friend Ackleyman might offer the wisdom: "Your rifle can't read a realoading manual." How true. Back in the day when i shot service rifle matches with an Armalite, the magic load was with a 69 gr Sierra Match bullet over 25 gr of 748 with no issues. The gun liked it just fine, but i wouldn't recommend it to others.

There are other factors, such as a slow lot of powder. i once gave away a couple of pounds of Accurate because it was unbelievebly slow burning and was some 6 grains over "max" in .243 without finding the max load. i figured the load would be only be good for that lot of powder and i'd have to start from scratch again with the next lot.

Then there's the deuce that's nicely accurate and loves 24.5 gr of R7 under a waxed 40 gr BK. Some folks gasp but there's so much freebore that the bullet is seated out so far to touch the lands that makes volume comparable to the .223 case. A compressed load with maybe half a caliber of bearing surface. No pressure signs other than the flattened WSR primers.

It can't be said too much that every rifle wants to be treated like an individual. i'm just a varmint guy who loads for accuracy instead of velocity, but sometimes one winds up with both. Beauteous maximus.
 
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