Used upper questions.

[t0xicsymph0ny]

So i just got a complete upper and tbh i dont know much about it. Has a keyhole mark on the reciever. Nothing on the handguard. The barrel has "6.5 grendel 1:8 SS" on it towards the end of the barrel. Anyway. My question how do i know what bcg to get for it. Is there a way i can determine type I from type II. Ive done some minor gunsmithing myself, but for ars i havent ever mounted a barrel. Dont just about everything else though. Ive got some calls out to local gunsmiths. One says he cant tell without having a bcg of either type. One more hasnt got back to me yet. Any suggestions?

[A5BLASTER]

Seems like it should be stamped on the barrel sammi or type II

Sounds like it has a no name, basement operation who knows what chamber.

Honestly you would probably safe money,time and lots if headaches if you pulled the barrel and trashed it and started over with a barrel from a well known supplier.

[lazyengineer]

Not ideal, but Well... I suppose one option is a a cheap standard (Type II) Grendel BCG can be had for $70. From what I can tell, the Type II is what the vast majority of Grendel's are. You could just buy that and try it, if it doesn't work, sell it for pretty much the same price and try again. I think it was.. Wilson? or some other name-brand that made the non-Type II style; which I imagine would be logo'd being a name brand.

https://www.bearcreekarsenal.com/bca-6-5-grendel-type-ii-bolt-carrier-group

[grayfox]

A type 1 barrel chamber (0.125 headspaced) with a type 2 bolt (0.136 bolt headspacing) is a recipe for overstretched and possibly ruptured cartridge, bad medicine.
If you don't have the go/no-go gauges and expertise you should take it to your gunsmith and have it checked there. Barrels can be replaced, fingers and eyes cannot.
Or like A5 says get a decent barrel from a known good mfr and start from there. You will be glad you did.

[t0xicsymph0ny]

IMG_20191119_211728.jpg
IMG_20191119_211701.jpgIMG_20191119_211623.jpg
forgot pics. So basically if no gunsmith around, buy a bcg and go/no-go gauges? that will show if the bcg i buy is good yeah?

[sbowhuntr]

The barrels roll stamp looks to be a bear creek arsenal which is no surprise.. The gas block is not bear creek either is the barrel nut, most likely a franken build. Most bear creek barrels I have seen in 6.5g are type 2 but you never know..

[Klem]

The gear in the photos appear to be in good condition.

I would buy a BCG and fire a round from the hip for safety. Then measure the headspace of the spent case.

If factory ammo does not go into battery then there's too little headspace and there's no danger because you won't be able to fire it. If it does go into battery then it is either OK, or too much headspace. If too much headspace you will know this when you measure the stretch in the case. If there is so much headspace that the chamber can't support the case on firing then it will rupture at the weakest point; the middle. This won't be as dangerous as a too-hot load however. It will be a bit louder and more smoke than usual will come out of the receiver. It's not pleasant if you are not expecting it and not helpful to the gun but it's not going to blow the gun to pieces. I have had two case separations and all it did was leave a slight trench in the chamber at the place where the case split - like a shallow plasma cut. I kept shooting it for a few years with no issues.

Firing the first round from the hip while looking away is something I do with all new barrels anyway, just in case. You can buy headspace gauges to avoid the guesswork but for a one-off situation like yours I would save the money and hip-fire it.

[kpswihart]

You can rent go / no go gauges here https://4drentals.com/product/264-lbc-ar-grendel-copy/. May be an option for you.

[VASCAR2]

Toolcraft BCG get very good reviews for about the same price as BCA. I’d buy a Toolcraft before BCA.

[A_National_Acrobat]

I'll 2nd the Toolcraft. I have a couple in different uppers 1st class all the way. & They make them for some pretty big names in the AR world. Those companies just laser etch their logos on them & charge $40.00 more for a Toolcraft.

[FLshooter]

I would not waste my money on a BCG till I knew whether it is a t-1 or2. I’d go to a smith.They will tell you.T-1 get a 7,62x39 bolt.T-2 get a Grendel bolt.

[LR1955]

I would not waste my money on a BCG till I knew whether it is a t-1 or2. I’d go to a smith.They will tell you.T-1 get a 7,62x39 bolt.T-2 get a Grendel bolt.

Why not? There is no difference in bolt carriers.

A gunsmith can only tell if it is a .125 or .136 recessed bolt if they have the bolts and headspace gauges for the Grendel.

Better he get the true Grendel bolt (.136" recess) and do like Klem stated in a previous post. Get a factory load and see if it chambers. Given a true .136" recessed Grendel bolt, it a factory load doesn't go into battery then he needs the .125" recessed bolt. If the round chambers then shoot it and look at the brass to see if it has ballooned out or if it appears normal. I deliberately shot some brass this way to see if I could pack a bit more powder into the resulting stretched case. The experiment failed but I got a good look at brass shot out of a chamber cut for the .136" recess using a .125" bolt. It was pretty obvious. The shoulder and neck area was stretched out and quite a bit rounded.

I do not see any other way he can find out unless he can identify the barrel maker and then ask them. Problem is most barrel makers make both types.

LR55

[lazyengineer]

The gear in the photos appear to be in good condition.

I would buy a BCG and fire a round from the hip for safety. Then measure the headspace of the spent case.

If factory ammo does not go into battery then there's too little headspace and there's no danger because you won't be able to fire it. If it does go into battery then it is either OK, or too much headspace. If too much headspace you will know this when you measure the stretch in the case. If there is so much headspace that the chamber can't support the case on firing then it will rupture at the weakest point; the middle. This won't be as dangerous as a too-hot load however. It will be a bit louder and more smoke than usual will come out of the receiver. It's not pleasant if you are not expecting it and not helpful to the gun but it's not going to blow the gun to pieces. I have had two case separations and all it did was leave a slight trench in the chamber at the place where the case split - like a shallow plasma cut. I kept shooting it for a few years with no issues.

Firing the first round from the hip while looking away is something I do with all new barrels anyway, just in case. You can buy headspace gauges to avoid the guesswork but for a one-off situation like yours I would save the money and hip-fire it.

This. People way overstate the safety hazard of excessive headspace. If the headspace is too long, the case stretches, and you can tell with calipers easy enough. If the headspace is way way too long, and casing already weak - then it just breaks in the middle. Not ideal, but it won't Kaboom and blow off fingers. The last 1/4" (before the head), is all it takes to swell and seal the casing from blowing out past the bolt. Casings are designed to start getting thicker after the middle section, just for this - so that if they do overstretch and break - they break in the middle rather than by the head. I've had and seen more headspace separations / broken shells than I can count. For the most part it's a non-item. Obviously I wouldn't just keep firing it like that, but one or two isn't a big deal.

[just_john]

+1 to Klem

[Herzo]

I have 2 barrels with bolts from the same supplier. Both are type II bolts with type I chambers. I didn't realize the problem until I started getting head seperations. One is a 6mm & the other a 6.5. I have had to be careful to only bump the shoulders back by 0.003" when I resize the brass.
Once I go through this lot of brass, I'll be changing to a type I bolt on the 6, but the 6.5 will require removing of the barrel extension and machining the interface since I would like to keep the stronger designed bolt on it. I'll also need to plug and relocate the gas port since it will need to be indexed ~60?.