Optimal Barrel Length for XCR 6.5 Grendel pistol?

[MeatAxe]

Have been thinking about pulling the trigger on a Rob Arms XCR pistol in 6.5 G. Starting with a pistol so I can legally convert it to a rifle and back again to a pistol, if I choose, without jumping through a lot of batf hoops.

Just wondering what the optimal length would be for a self defense pistol / truck gun in 6.5 Grendel?

Thanks!

[Huckleberry75]

Several of us here have used the Monster 12" bbls and have seen very acceptable accuracy and potency. The 12" is more than capable of taking deer out to 300yds with the right bullet selection and is still very handy for "truck travel". You will highly prefer that length barrel to be suppressed, just an FYI.

[VASCAR2]

I have 12” 6.5 Grendel and for a pistol I think it strikes a good balance for size and performance. If you go to a rifle then you need 16” minimum length barrel so I guess you could use a pin and welded 14.5” to get 16” length on a pistol lower. I personally would rather have a full 16” barrel for the extra velocity than a 14.5” or shorter P&W to 16”.

I never did like switching uppers and every lone upper morphed into a complete firearm. In some jurisdictions where it is difficult to get a license for each firearm I might see the utility of using one lower. This is just my opinion and not legal advise but I see the NFA SBR as a disadvantage because I live close to the state line. I don’t want the NFA hassle if I want to shoot with my brother in another state.

[Jakegsxr11]

I have a 12" monster barrel and it works quite well. That being said there is nothing optimal about a 12" barrel. The shorter you go the more you sacrifice in performance vs portability.

[MeatAxe]

Thanks for that information, guys!

One of the advantages of the XCR is the ability to change barrels / convert to other calibers with relative ease. The barrel is attached to the receiver by one readily accessible bolt.

[LRRPF52]

Depends on what upper receiver length you go with for the XCR.

There’s a mini and a micro for the shorties. When you configure on a Mini upper, it only seems to allow a 10” barrel.

[MeatAxe]

^ Good point - will need a “medium length” receiver that will accommodate both pistol and rifle-length barrels. Would probably get an additional 12” 7.62x39 barrel since they don’t lose much velocity compared to a rifle length bbl. and share the same bolt / carrier with the 6.5 G.

[A5BLASTER]

^ Good point - will need a “medium length” receiver that will accommodate both pistol and rifle-length barrels. Would probably get an additional 12” 7.62x39 barrel since they don’t lose much velocity compared to a rifle length bbl. and share the same bolt / carrier with the 6.5 G.

They dont share the same bolt.

[MeatAxe]

They dont share the same bolt.

That’s funny, the Rob Arms parts catalog says they’re one and the same bolt for both calibers, which would make sense, since 6.5 Grendel is derived from 7.62x39.

Maybe the AR platform requires different bolts for these two calibers? I have no idea.

[VASCAR2]

Depends on whether the barrel is chambered to use .125” bolt face depth or .136” bolt face depth. As long as the 7.62 and 6.5 Grendel are machined to accept the same depth bolt face they are the same. Original Colt 7.62x39 AR-15 used a .136” bolt face depth to get more metal in the extractor. Most of the AR-15 market went with .125” bolt face depth with the 7.62x39. The 5.56/223 AR-15 bolt has a .125” bolt face so was not changed for some 7.62x39 AR-15 barrels.

The AK chambered for 6.5 Grendel use the same bolt as 7.62x39 AK’s.

[Huckleberry75]

Sounds like they went with the MK 1 (.125") bolt pattern instead of the more common MK2 (.136")

[MeatAxe]

Depends on whether the barrel is chambered to use .125” bolt face depth or .136” bolt face depth. As long as the 7.62 and 6.5 Grendel are machined to accept the same depth bolt face they are the same. Original Colt 7.62x39 AR-15 used a .136” bolt face depth to get more metal in the extractor. Most of the AR-15 market went with .125” bolt face depth with the 7.62x39. The 5.56/223 AR-15 bolt has a .125” bolt face so was not changed for some 7.62x39 AR-15 barrels.

The AK chambered for 6.5 Grendel use the same bolt as 7.62x39 AK’s.

Sounds like they went with the MK 1 (.125") bolt pattern instead of the more common MK2 (.136")

Well, you’ve got me. The Rob Arms parts catalog for the bolt says something like “7.62x39 Type 2 (Note: same as 6.5 Gren).” Of course, the XCR has a more AK-like 3 big lug bolt compared to the AR Type smaller multi-lug bolt.

[VASCAR2]

I didn’t look at Rob Arms website and have not looked at the XCR platform. I was just referring to the AR-15 pattern and what bolts have generally been used with the 7.62x39 or 6.5 Grendel. Black Hole Weaponry coined the term Type I for bolts with .125” bolt face depth and Type II with .136” bolt face depth. A barrel chambered to use a .125” bolt will probably have excessive head space if a .136” bolt face depth bolt is used.

It’s possible to chamber a 7.62x39 barrel to use a .136” bolt as Colt originally used .136” bolt with their 7.62x39 AR-15’s. Rob Arms might in fact be using the same .136 bolt for both 7.62x39 and 6.5 Grendel.

[LRRPF52]

Gents, the OP is talking about the Robinson Arms XCR, not the AR-15.

It has a much larger bolt with a huge extractor, and huge bolt lugs:



None of the AR-15 constraints apply to the XCR. Totally different designs.

It also has different types of Op Rods, gas blocks, gas tubes, and pistons.