ar-10 clone jamming

[CPorter]

I have taken my DPMS LR-243 to the range a couple of times recently and had it jam to the point were I had to use a rubber mallet to get the bolt to release. From the condition of the brass it appears the brass is catching at the body/shoulder junction. The first time happened after about 23 loads the second after about 17. These are reloads, full length resized and the cases free of case lube. Accuracy and function seems to be fine to this point. The gun is delivering 1/2 moa groups when using my reloads. I fed two boxes of factory load through the gun previously without significant jams or failures to feed. Any ideas on how to get it to work better?

The brass was full size resized in good RCBS dies that I bought in the 70s.,They've worked for all the bolt action guns) Load is on Frontier brass that's been fired maybe 4 times and full size resized prior to using as recommended in automatics, 43.5 to 44.1 grains IMR-4350, Fed 215 primer, Nosler 70 gr ballistic tip WS2 coated. The loads were running 2990 to 3056 fps with 43.9, 44.1 and 44.3 grs of powder.

 

[SooStan]

I don't understand what is jamming. Maybe a better description or picture of the jam. Failure to extract, feed etc.

 

[fdshuster]

If the brass had been previousely fired in another 243 chamber, the diameter of that chamber, at the case head, may have been larger than the chamber diameter on your AR-10: a difference of .002" can stop the round from fully chambering. This is an area that the standard full-length die will not reduce in dia. Try new, unfired brass and/or factory ammo. If your case head dia. is too large for your chamber, you could use a small base die, as made by RCBS.

 

[CPorter]

The jam happens when the previous fired case ejects and the newly fed rounds goes into the chamber but stops short of full bolt closure. Enough for the bolt to cam over and lock the chamber but not fully seat or fire.

Prior to firing the loaded rounds would feed into the chamber fine but once hot they grab at the shoulder area.

 

[Greg110]

Check your chamber for dirt/roughness of any sort. I have seen A15's with Parkerizing in the chamber,not good. You might try using a tight fitting bore mop with JB to clean/polish the chamber.

 

[people]

You probably need a small base die.

 

[SooStan]

Do you have an ammo gauge? Does factory ammo work? There is something that is different with the ammo. The base is to large, donut in the neck, long neck, a gouge in the brass from the magazine or barrel extension. Measure everything. I had a bolt action once that I bought used and it had a lot of buildup in the chamber at the shoulder. Caused serious problems until I sprayed brake cleaner and used a good patch to clean it.