260 AI problems with Green Mountain barrel

[jdscada]

Hello everyone, I have an issue that basically has me scratching whatever is left of my hair off. Have a Green Mountain 260AI barrel that is threaded for Savage Large Ring. I have done the following:

* Cleaned up threads on both action and barrel and applied light grease to barrel threads.
* Screwed in barrel nut all the way in and inserted recoil lug with notch facing action like normal.
* Removed bolt from action and removed firing pin and ejector to insure correct head spacing with gauges.
* Inserted bolt back into action minus firing pin and ejector with Go gauge. 260AI Forster gauge GO
* Carefully screwed in action until barrel/chamber makes positive contact with Go gauge, backed off a hair to leave room for barrel nut torquing.
* Checked with NoGO and bolt does not close, so good. 260AI Forster gauge NoGo
*Torque barrel nut down carefully to 65 ft lbs
*Checked once again with Go Gauge, all good, bolt closes perfectly.
*Checked once again with NO Go gauge, all good, bolt does not close
********************Here comes the weird part*************************

Go to get 260 remington modified case for hornady lock N Load just estimate seating depth, and this is an estimation since I have not fireformed brass yet for this setup.

Modified case goes in and closes with bolt, regular 260 remington case with Hornady 140 gr Amax (dummy round) will not enter throat of chambering correctly. This is basically the same case, it goes about 3/4 way in and seizes, push bolt up into it and does not enter, then I have to jam bolt back to remove brass which is latched by extractor.

Tried 260 remington, and norma brass with no luck, only the 260 modified case goes. Barrel is stamped 260AI, but I get this eerie feeling that it's a 260 Remington, however, I still can not explain why a dummy round that I have from another 260 remington will not go neither.

Am I losing my mind???

attached photo shows in order, 260 rem modified case for Hornady LocknLoad, 260 rem dummy round, 260AI Rem, 260AI Norma.

Also notice scarring on other three rounds that will not chamber.

Thanks for any help everyone.

 

[FilippoMo]

Did you full lenght size the cases before chambering?
Filippo

 

[dkhunt14]

If you didn't resize the cases they may be too big at back end for chamber. They could have been shot in a gun with a bigger chamber. If you sized them and they did that, either your die isn't sizing enough or the gun was chambered with a tight at back end reamer. Matt

 

[Ggmac]

Use new brass ?

 

[jdscada]

New brass and I ran them through full length sizing die (Redding 260 improved 40 Deg Die)

 

[BoydAllen]

I would remove the barrel and do a chamber cast with Cerrosafe, following the directions carefully as to when to measure, then I would compare the dimensions with a chamber drawing and if they did not match, have a conversation with whoever chambered the barrel about reamer dimensions.

 

[jdscada]

Little update, adjusted full length die to insure that I was full lengthing the whole cartridge, and not much change. So I thought maybe it's tight chamber or short chamber, so I starting trimming brass back, had to go to 1.93" before bolt would attempt to close, and it will with a little effort, however, rubber mallet needed to extract. Notice updated pictures with trimmed brass in the middle, 1.99" brass new but full length, and a regular dummy 260 remington. I'm at a loss right now.....

Not familiar with the chamber cast with Cerrosafe, I will have to look it up.

Thanks again for all your input guys.

 

[savagedasher]

Take a new 260 case not sized will it close in the action ? If it won't' you have a chamber problem . Larry

 

[IdahoCTD]

I would blacken the whole case and bullet with a black sharpie and try to chamber it to see where it is rubbing. You could have a tight neck that requires turning, it could be a short throat, or tight at the back of the chamber. A casting would help, as has been mentioned, as well. With a blackened case/bullet it should help narrow things down a bit anyway.

 

[jdscada]

I will give these a try right away and be back with an update. Thanks

 

[dkhunt14]

How far are you bumping the shoulder when you resize? Were these cases shot in another gun? I would try a new 260 case. Matt

 

[jonbearman]

If the barrel was used, it may have a neck that broke off a case while extracting from the former owner. I would get it bore scoped to look at that chamber carefully and I think you will find your problem. Any good smith should have one and have him do the chamber cast if you don't get the concept straight away.

 

[jonbearman]

Matt he is using new brass.

 

[savagedasher]

If a new parent case wont fit he has a problem. Larry

 

[jdscada]

Ok, another update. painted up a brand new brass after running through full length die, definitely have resistance when trying to chamber into barrel, cannot close bolt. Tried chambering regular 260 with bullet, resistance in same spot on brass, managed to close bolt with some effort but had to beat it out with rubber mallet.

I have also removed action again, started over, inspected throat on barrel, seems fine, however, I am not a professional and do not have a borescope, however, I have access to a digital borescope at work that I can run in there to inspect and take pictures and video.

anyways, I removed recoil lug, it measures .25" thickness, and used a slightly thinner one .18" just to experiment, (my version of thinking outside the box), and same results.

Is there any possibility that maybe the Forster die is not full lengthening correctly?? It seems after I run it through, it leaves back 3/8 of it is not touched or marked up, I have press setup where bottom of die and shell holder are already touching, never usually run this tight, usually keep a gap about the thickness of a nickel in between, but since I was second guessing the die, I ran flush, and have resistance when full lengthening.

 

[savagedasher]

Where is the marks on the Standard 260 ? if the parent cases doesn't fit . You have a problem. Pull the bullet out a new 260 cases. and it should close with ease. The chamber may be a tight neck. Larry
..

 

[jdscada]

Larry, the regular 260 does have marks on the bottom of the case, however with some effort it will chamber but extremely tight and has to be beaten out with rubber mallet, I can try a untouched 260ai brass but get same results. I know it sounds odd that I'm saying its untouched 260ai brass, but some time ago, I received a bunch of 260 brass that is branded 260 but has improved shoulder already, however, it's flawless, primer holes, entire round seems brand new, does not look like once fired brass. I only have one 260 with a bullet on it, but it's a dummy round from another 260 barrel that I have and guy sent me a sample, but the barrel I'm dealing with right now is stamped on barrel from GM 260AI. So, I'm a bit baffled, as parent case which is 308, I do have some of those, and I have 7mm-08 which is still within same parent case, and I have alot of 260 brass but all of it has improved shoulder, which is crazy because most of it seems brand new and never fired but it definitely has improved shoulder compared to regular 260 remington.

thanks again for all the input..................

JD

 

[MattPeetz]

I would venture a guess that you have a Match AI chamber and the reamer used is out of spec (smaller) since it leaves marks on brand new unfired regular 260 brass. Any brass that was used in a saami spec chamber has a potential to not work and can try to resize it with a small base body die.

 

[jdscada]

I found out who actually gunsmith is from person I purchased barrel from so I guess it's time to give him a call to see what specs he used to chamber this barrel. Dang it, and I was an eager Beaver to get this setup and go put some rounds on paper to see how it does, although weather is not cooperating, once again, that's shooting......................

 

[savagedasher]

What I want you to do is take a new un fired and un touch 260 brass see if it will chamber. If it sticks then see where the marks are. it sounds like you have a tight neck. if that the case you will see on the neck only marks.
Larry