Short Stroke 260 Rem

[Flux Capacitor]

I took some once fired 308 cases and formed them into 260 Remington. Loaded them up with 37 and 38 gr of BLC-2 and 120 gr Sierra bullets.

Shot them out of an Armalite 260 upper (AR10 based) and they short stroked. The cases stayed inside the chamber after each firing, or ejected but failed to chamber another one. There was not enough power to cycle.

I then fired factory 260 Remington loads from the store and they all worked perfect and cycled fine.

What could be the problems with my reloads? I started from the bottom of the chart and even added one more grain to the second batch. All of which failed. Any suggestions?

[FLIGHT762]

Could be that the necks are too thick and stick to the chamber after being fired. I reload for 260 and I found necking 308 brass down to 260 makes the necks too thick.

To make 260 brass, I neck up 243 cases using a tapered expander. It works fine, although cases will be a tad short. Some like to neck down 7-08 cases.

[FLIGHT762]

A way to check to see if the necks are too thick; take a couple of the fired necked down 308 cases. Take a 6.5 bullet and see if it passes easily through the fired case neck. If there's any resistance, the case necks are too thick.

[Flux Capacitor]

Wouldn't a thick neck have chambering problems before firing? I am having problems after firing.

[FLIGHT762]

Your loads of BL-C(2) may be too light. Work slowly up to max.

I tried necking down 308 cases to 260 and the necks are too thick. I stopped the practice.

Your issue may be a combination of both. Check your fired reformed 308 case necks with one of your 6.5 bullets and see if you have clearance. The 6.5 bullet should slide into the fired case neck with no resistance. If there's no resistance, slowly increase your charges to see if you get proper functioning.

If your reformed 308 case necks are too thick, you are going to have pressure problems before you get to max.

I've found that powders in the slower burning rates such as W-760, REL-19, IMR 4831, gave higher velocities even with the 120 gr. bullets.

[Flux Capacitor]

Flight, I suspect my AR10(Target) upper has a very tight chamber. I put a 6.5 bullet in the fired cases. The bullet has resistance with both fired factory 260 brass and the fired formed 308 brass.

Some of the 308 brass has more resistance than others.

[FLIGHT762]

I would try some 243 cases expanded up to 260. You shouldn't have to neck turn your factory 260 cases or 243 cases. I found 308 cases didn't work well for me. I would try Winchester 243 cases if you can get a few once fired to experiment with. Winchester has thinner case necks compared to some other brands.

The AR-10 style gas guns can get finicky with what ammo they like. My SR-25 has a snug chamber. I was blowing primers with one lot of factory loaded .308 Hornady TAP 168 A-Max. It functions fine with 168 bullets, but when I tried some Hornady TAP 155 A-Max factory ammo, I was getting short stroking. The gun just didn't like the 155's.

[Flux Capacitor]

I would try some 243 cases expanded up to 260. You shouldn't have to neck turn your factory 260 cases or 243 cases. I found 308 cases didn't work well for me. I would try Winchester 243 cases if you can get a few once fired to experiment with. Winchester has thinner case necks compared to some other brands.

The AR-10 style gas guns can get finicky with what ammo they like. My SR-25 has a snug chamber. I was blowing primers with one lot of factory loaded .308 Hornady TAP 168 A-Max. It functions fine with 168 bullets, but when I tried some Hornady TAP 155 A-Max factory ammo, I was getting short stroking. The gun just didn't like the 155's.

Thanks Flight. Can I just run the 243 brass through my 260 dies? Or do I need special tools?

[Fjold]

Just mic the diameter of the neck of a fired factory case. This will give you the measurement of your chamber's neck diameter (within .002, or so) then measure the neck diameter of your reloaded ammunition. If the reloads are smaller than the fired factory rounds then you're fine.

37 grains of BL-C(2) is the minimum load for 120 grain bullets, max is 40 grains.

[FLIGHT762]

Thanks Flight. Can I just run the 243 brass through my 260 dies? Or do I need special tools?

Just lube the inside & outside of the 243 cases and run them through the 260 die. I use a tapered expander, it makes the necking up go smoother. I use RCBS 260 dies. I gave RCBS a call and they sent me a tapered expander free.

[Flux Capacitor]

Ill take measurements tonight

[EmmaGoldman]

If you want to check neck thickness, just mike the outside of the neck with a bullet seated. If it's under .2969" you're fine. As long as you're within SAAMI spec on the loaded cartridge it should function fine.

I'd guess a heavier load will fix it (but measure first).

[Flux Capacitor]

If you want to check neck thickness, just mike the outside of the neck with a bullet seated. If it's under .2969" you're fine. As long as you're within SAAMI spec on the loaded cartridge it should function fine.

I'd guess a heavier load will fix it (but measure first).

Its .2955

[Flux Capacitor]

Just mic the diameter of the neck of a fired factory case. This will give you the measurement of your chamber's neck diameter (within .002, or so) then measure the neck diameter of your reloaded ammunition. If the reloads are smaller than the fired factory rounds then you're fine.

37 grains of BL-C(2) is the minimum load for 120 grain bullets, max is 40 grains.

Factory Fired #1 - 0.296
Factory Fired#2- 0.296
Reload (308 brass) #1- 0.295

I am at a loss here. I don't have a chambering problem. Could the neck still be an extraction issue?

[EmmaGoldman]

I am at a loss here. I don't have a chambering problem. Could the neck still be an extraction issue?

I seriously doubt it. Neck measurement is fine.

You have ruled out one possible problem, so work on the other possibility.

Bring the powder charge up slowly and pay close attention as you go.