While I've been very impressed with the XCR, the only thing holding me back from purchasing one is the 1:9 twist rate since I plan to use 77 gr bullets. From a previous post, I understand RobArm does not offer 1:7 as an option. Has anyone had experience with having an aftermarket barrel made for the XCR??
1:7 Twist XCR Barrels
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Alex has been muttering about getting 1/7 going. Who knows where the road may lead. 
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Dunno. My barrel is 1/8. Stabilizes everything I use in it. <shrug>
Your XCR has a 1:8 barrel?? I didn't know they made them. That would probably be OK (though not optimal) for 77 gr but 1:9 is not.
Or how long it will take to travel it!Alex has been muttering about getting 1/7 going. Who knows where the road may lead.
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I payed $50 extra for the 1/8 twist heavy barrel... but when it showed up to my dealer, it was a 1/9 twist heavy barrel I eventually got over it.
I really don't see the point of 1/9 twist barrels as none of us shoot anything below 55gr anyways. Only specialty built Varmint AR's(or other 223) should be 1/9 twist.
I eventually got over it.I really don't see the point of 1/9 twist barrels as none of us shoot anything below 55gr anyways. Only specialty built Varmint AR's(or other 223) should be 1/9 twist.
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My last XCR could handle palm sized groups out to 200 yards with Prvi 75gr HPBT. 1/9 pencil + TA01NSN
One of the perks of working with LEO is seeing what does best after extensive tax payer funded testing. MK262 and other heavy match type ammo are highly overrated as self defense tools in the environments and scenarios typically encountered by civilians and LEO. For this reason and based upon the feedback of some very imformed professionals, I use LE223T3 62gr BSP regardless of twist in all my carbines currently
One of the perks of working with LEO is seeing what does best after extensive tax payer funded testing. MK262 and other heavy match type ammo are highly overrated as self defense tools in the environments and scenarios typically encountered by civilians and LEO. For this reason and based upon the feedback of some very imformed professionals, I use LE223T3 62gr BSP regardless of twist in all my carbines currently
Feel free to correct me but it's my understanding that when the 61.7 gr SS109 NATO round was introduced, FN recommended a 1:7 twist to achieve optimal stability and accuracy from 50 to at least 600 yards. The US subsequently changed the twist in the M16/M4 platform to 1:7 for this reason. While I agree that usually LE and Mil requirements are similar, Mil generally emphasizes single shot accuracy over a wide range of distances while LE is more interested in laying down a maximum amount of lead to neutralize a threat at much closer distances. So given the option of having a weapon with a twist (1:9) that is fine for LE purposes or the same weapon with a twist (1:7) that is just as effective at close distances and also has the ability to put a single accurate shot on target at greater distances, the latter option seems more reasonable.
Bottom line is that 1:7 is suitable for any scenario with any ammo from 55 to 77 gr while 1:9 is not.
Bottom line is that 1:7 is suitable for any scenario with any ammo from 55 to 77 gr while 1:9 is not.
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Youy are correct, though many shooters will go with 1:8 which provides the same degree of stabilization and allows the same range. It is also closer to the 1:7.7 which is ideal for 75-77g tips.
Contrary to some opinions, you can never have too much accuracy.
Contrary to some opinions, you can never have too much accuracy.
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1/7 was not introduced for M855/SS109 type ammo. 1/7 is for the L110 (M856) tracer round.
1/7 has no inherent accuracy advantage. I've attended my fair share of matches where 1/9 and 1/8 shooters ran circles around solid 1/7 shooters. A steady eye, hand and match grade bullet has more to do with accuracy than twist alone.
1/7 has greater compatability on the heavy side, while 1/9 is the higher side. Mid range between 55gr and 75gr is very close.
Another point is, and this is not directed at you, there are plenty of people wailing about 1/7 and their need for it because of accuracy and lethality, and then spend all their time shooting white box specials at 25 yards, and have no idea how match type MK262 bullets perform in self defense situations they will likely encounter.
I'd like for Robinson to at least offer the 1/7 as an option, but I openly admit it would make little difference in the way I use the XCR. I would still use LE223T3 for self defense, and use my high end custom rig for attempts at 500 yard work.
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I will admit, I have only ever shot 1 box of 77gr in my life (so far), but the point is we want our gun to be able the 77gr on demand. Forget the fact that 99% of all the ammo I have put through my AR is 55 and 62 gr, I just want a barrel that covers the range of ammo that I shoot, and 1/9 does not do that. It does it 99% of the time, but not 100%
I just recently bought 500 projectiles of SMK 69gr because I only have one rifle that is 1/7 twist, my Noveske. I want to be able to shoot this bullet in all my 223's and not just the Noveske, hence the reason I bought 69gr over the 75gr.
I just recently bought 500 projectiles of SMK 69gr because I only have one rifle that is 1/7 twist, my Noveske. I want to be able to shoot this bullet in all my 223's and not just the Noveske, hence the reason I bought 69gr over the 75gr.
Variable:
My original post was not to solicit opinion as to the relative merits of various twist rates (though I have no problem with people expressing those opinions) or to get into a p****** contest with others regarding the relative merits of each twist. If you will re-read the original post, you will note that I asked for input from people who had had an aftermarket barrel in 1:7 twist made for their XCR, having already made the decision that for my dollars I wanted a rifle that that was accurate at various distances from close in to long range with any effective bullet weight (55-77 gr) that I might choose.
That said, you may wish to read the extensive, multi part review of the development of the 5.56x45 cartridge by Gil Sengel in Handloader magazine. It was only after the development of the SS109 that the army went to 1:7 twist after first resisting the move. While it is true that the tracer round (being heavier and therefore longer) requires a faster twist, the impetus to change the twist was the SS109 round. If you have references to the contrary I would appreciate your citing them.
Secondly, comparing accuracy of twist rates by the results of different individuals shooting different twists in different rifles at a competition and expecting a valid conclusion is not very objective. If you can cite a true comparison (perhaps from the LE sources you refer to) of the accuracy of various twist rates with different bullet weights at various ranges under controlled circumstances, I would be delighted to read them.
Thirdly, the fact that you are happy with 1:9 twist in your XCR doesn't mean that others don't have different requirements.
Mickey C:
Thumbs up - in any weapon deserving of the name, accuracy is only secondary to reliability.
My original post was not to solicit opinion as to the relative merits of various twist rates (though I have no problem with people expressing those opinions) or to get into a p****** contest with others regarding the relative merits of each twist. If you will re-read the original post, you will note that I asked for input from people who had had an aftermarket barrel in 1:7 twist made for their XCR, having already made the decision that for my dollars I wanted a rifle that that was accurate at various distances from close in to long range with any effective bullet weight (55-77 gr) that I might choose.
That said, you may wish to read the extensive, multi part review of the development of the 5.56x45 cartridge by Gil Sengel in Handloader magazine. It was only after the development of the SS109 that the army went to 1:7 twist after first resisting the move. While it is true that the tracer round (being heavier and therefore longer) requires a faster twist, the impetus to change the twist was the SS109 round. If you have references to the contrary I would appreciate your citing them.
Secondly, comparing accuracy of twist rates by the results of different individuals shooting different twists in different rifles at a competition and expecting a valid conclusion is not very objective. If you can cite a true comparison (perhaps from the LE sources you refer to) of the accuracy of various twist rates with different bullet weights at various ranges under controlled circumstances, I would be delighted to read them.
Thirdly, the fact that you are happy with 1:9 twist in your XCR doesn't mean that others don't have different requirements.
Mickey C:
Thumbs up - in any weapon deserving of the name, accuracy is only secondary to reliability.
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I tend to shoot 62g mostly, but there are two exceptions. I also have to be aware that my 62g groups aren;t as tight as my 77g but I prepare for this when practising.
For competition or long range shooting I use 77g. It handles the wind a lot better than 55 or 62 and groups better with a 1:7/1:8 barrel, particularly at range.
For self defense I use 55g. I want max velocity to ensure fragmentation on impact.
What you shoot in practice isn't as important as what you shoot for real (defense, offense or sport) assuming we can't all shoot top grade ammo all the time. Having one rifle which can do all these in the chosen caliber is a real bonus.
My 16" 1:7 AR outshoots my 1:9 XCR everywhere except at 100 yards. At 200 it is tighter and noticibly so at 300.
For competition or long range shooting I use 77g. It handles the wind a lot better than 55 or 62 and groups better with a 1:7/1:8 barrel, particularly at range.
For self defense I use 55g. I want max velocity to ensure fragmentation on impact.
What you shoot in practice isn't as important as what you shoot for real (defense, offense or sport) assuming we can't all shoot top grade ammo all the time. Having one rifle which can do all these in the chosen caliber is a real bonus.
My 16" 1:7 AR outshoots my 1:9 XCR everywhere except at 100 yards. At 200 it is tighter and noticibly so at 300.
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Exactly my point.
If I can sort of paraphrase Pat Rodgers, we need to get away from the romantics of twists, or whatever other minutia the gun community has become so enamored with, and focus on shooting smelly bearded men in the face.
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That's a great quote!
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I cant take credit for it. That's all Pat.
And for what it's worth, I've been saying longer than anyone probably that the XCR should have a 1/7 option. I just posted a thread about recommended improvements a few weeks back saying 1/7 is a good idea, and there isnt a really good reason for not offering 1/7
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I'm a painter.
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