Anyone have good sucesss running 77 SMK's in an AR ? - Page 3

Metal god · May 22, 2015, 09:47 PM

Very cool Glad it worked out . I'll be doing my own test this weekend from a 1-9 16" barrel . Only to 300yds though . These will be my reloads that I only get 2560fps from a 20" barrel 1-8 twist . I'll report back

Road_Clam · May 23, 2015, 08:51 AM

Quote:

Originally Posted by Metal god

Very cool Glad it worked out . I'll be doing my own test this weekend from a 1-9 16" barrel . Only to 300yds though . These will be my reloads that I only get 2560fps from a 20" barrel 1-8 twist . I'll report back

I took the opportunity of having my crono set up and reading favorably to test some factory American Eagle AR 5.56 ammo through both my Varmint 24" upper and my std 16" upper. Was curious about the velocity differences. Here's the data I gathered :

American Eagle AR 5.56 ammo advertised velocity : 3165 fps

16" bbl Bushmaster 1-9" upper:
low=3051 , Hi=3103 , avg=3077 ES=52 SD=21

24" bbl 1-9" Varmint upper :
Low=3295 High=3425 Avg= 3360 ES=71 SD=49

So there's an additional 280 fps through my 24" bbl which seems a lot but this is the data I got so I'm going with it. Data shows that the AE AR 5.56 ammo is pretty hot stuff.

Metal god · May 23, 2015, 08:56 AM

Well they say you can get 30 to 50fps more per inch of barrel length . It would seem you're right in that window . Those results seem reasonable and accurate to me . Thanks for showing the results

**Unclenick** · May 23, 2015, 02:42 PM

This is a general approximation I came up with based on expansion ratios for different barrel lengths. It lands within 20 fps in this case. Given differences in powders, chambers, and bore conditions, I think it did pretty well, if I do say so myself:

3360 fps × 0.91 = 3058 fps.

Road Clam,

That's a vexing situation you have with that barrel. A bore scope would tell you if you have a defect of some kind, or if you failed to achieve adequate bore smoothing because of copper shielding of the barrel. That would tend to be within the first three inches or so past the throat, if it happened. Slugging will tell you if that barrel has a constriction that still needs to be removed. Barrel blanks not stress-relieved before contouring often have tighter bores where the steel is thickest, back near the chamber. I agree that with a bore that fouls that fast, fully cleaning after every lapping round for the first ten might have been a good idea, then every five after that. You could still do the Iosso or JB and then Flitz routine, of course, which won't introduce any copper as you do it.

If you go to a new barrel, a barrel you know has been stress relieved prior to contouring or one that has been hand lapped would be a good choice. Anything made from a Douglas blank will have been stress-relieved. Criterion barrels are all hand-lapped and are a good option for something less expensive than the custom makers turn out. A Kreiger will cost you an extra $70, but are cut rifled and hand-lapped and are a mainstay among match shooters. The lapped finish is finer in the Krieger I own than in the Criterion barrels I've bought. The Criterions get the Iosso/Flitz treatment from me, and I usually touch my crowns up slightly, but that's me being compulsive and not because I have any scientific evidence that it's necessary.

Road_Clam · May 23, 2015, 08:37 PM

Uncle Nick, I'm confused at what your stating , why did you take my 24" bbl avg velocity and multiply it by .91 ? Do my numbers seem off ?

Metal god · May 23, 2015, 10:25 PM

If I may Unclenick ?

He was patting him self on the back

His calculations say if you have an ave muzzle velocity of 3360fps from a 24" barrel as you do . When you shoot that same ammo from a 16" barrel you should get an ave of 3058fps . Seeing how your results show an ave MV of 3077fps from a 16" barrel . His formula is pretty accurate because it's not only inside your ES it's inside your SD . That is a pretty good formula if you ask me .

oley55 · May 26, 2015, 12:08 AM

thanks Nick,

I think this part was for Oley versus Road Clam

Quote:

Road Clam,

That's a vexing situation you have with that barrel. A bore scope would tell you if you have a defect of some kind, or if you failed to achieve adequate bore smoothing because of copper shielding of the barrel. That would tend to be within the first three inches or so past the throat, if it happened. Slugging will tell you if that barrel has a constriction that still needs to be removed. Barrel blanks not stress-relieved before contouring often have tighter bores where the steel is thickest, back near the chamber. I agree that with a bore that fouls that fast, fully cleaning after every lapping round for the first ten might have been a good idea, then every five after that. You could still do the Iosso or JB and then Flitz routine, of course, which won't introduce any copper as you do it.

If you go to a new barrel, a barrel you know has been stress relieved prior to contouring or one that has been hand lapped would be a good choice. Anything made from a Douglas blank will have been stress-relieved. Criterion barrels are all hand-lapped and are a good option for something less expensive than the custom makers turn out. A Kreiger will cost you an extra $70, but are cut rifled and hand-lapped and are a mainstay among match shooters. The lapped finish is finer in the Krieger I own than in the Criterion barrels I've bought. The Criterions get the Iosso/Flitz treatment from me, and I usually touch my crowns up slightly, but that's me being compulsive and not because I have any scientific evidence that it's necessary.

Metal god · June 9, 2015, 01:14 AM

Went and shot my 16" 1-9 twist AR using Fed GMM 77gr and some of my 77gr smk reloads . I only shot to 300yds . The 1-9 had NO problem stabilizing them out to 300yds . It was very windy in the afternoon and I did not have my rifle fully zeroed so there was no real group per-say but I did have all 20 shots make little tiny perfect cicles in the paper .

myth further busted .

Road_Clam · June 9, 2015, 09:00 AM

Quote:

Originally Posted by Metal god

Went and shot my 16" 1-9 twist AR using Fed GMM 77gr and some of my 77gr smk reloads . I only shot to 300yds . The 1-9 had NO problem stabilizing them out to 300yds . It was very windy in the afternoon and I did not have my rifle fully zeroed so there was no real group per-say but I did have all 20 shots make little tiny perfect cicles in the paper . myth further busted .

Nice ! So is there a "double-dog-dare" to take 77's through a 1-9" 16" bbl AR out to 600 yds ? I might need to attempt this...

**Unclenick** · June 9, 2015, 09:19 AM

Oley,

Yes. My brain wandered and twisted down the path. Nothing new.

M.G.,

Glad to see another 1 in 9 shooting these things. It's a funny business that some have problems and some don't. Awhile back someone published something on rifling twist tolerances and they weren't all dead on. It would be interesting to learn if some 1:9's are actually 1:9.5 or some are actually 1:8.7 or some such thing.

Otherwise, it's different factors that account for the different results and it will take some work to sort them out.

Metal god · June 11, 2015, 03:18 PM

When I cleaned my 1-9 I went ahead and checked the twist rate . It appears mine is just over 1-9 . I measured a 9" space on my cleaning rod . When the first mark reached the receiver I marked the top of the back line . I then pushed the cleaning rod in until the back line was at the receiver . The mark on the top line did not quite make it all the way around . It was very close but not straight up on top . It needed about 3/32 more to go . Not sure what that would translate to or if there is that much fudge room in that method .

May 22, 2015, 09:47 PM	#51
Metal god Senior Member Join Date: April 10, 2012 Location: San Diego CA Posts: 6,876	Very cool Glad it worked out . I'll be doing my own test this weekend from a 1-9 16" barrel . Only to 300yds though . These will be my reloads that I only get 2560fps from a 20" barrel 1-8 twist . I'll report back __________________ If Jesus had a gun , he'd probably still be alive ! I almost always write my posts regardless of content in a jovial manor and intent . If that's not how you took it , please try again .

May 23, 2015, 08:56 AM	#53
Metal god Senior Member Join Date: April 10, 2012 Location: San Diego CA Posts: 6,876	Well they say you can get 30 to 50fps more per inch of barrel length . It would seem you're right in that window . Those results seem reasonable and accurate to me . Thanks for showing the results __________________ If Jesus had a gun , he'd probably still be alive ! I almost always write my posts regardless of content in a jovial manor and intent . If that's not how you took it , please try again .

May 23, 2015, 02:42 PM	#54
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,063	This is a general approximation I came up with based on expansion ratios for different barrel lengths. It lands within 20 fps in this case. Given differences in powders, chambers, and bore conditions, I think it did pretty well, if I do say so myself: 3360 fps × 0.91 = 3058 fps. Road Clam, That's a vexing situation you have with that barrel. A bore scope would tell you if you have a defect of some kind, or if you failed to achieve adequate bore smoothing because of copper shielding of the barrel. That would tend to be within the first three inches or so past the throat, if it happened. Slugging will tell you if that barrel has a constriction that still needs to be removed. Barrel blanks not stress-relieved before contouring often have tighter bores where the steel is thickest, back near the chamber. I agree that with a bore that fouls that fast, fully cleaning after every lapping round for the first ten might have been a good idea, then every five after that. You could still do the Iosso or JB and then Flitz routine, of course, which won't introduce any copper as you do it. If you go to a new barrel, a barrel you know has been stress relieved prior to contouring or one that has been hand lapped would be a good choice. Anything made from a Douglas blank will have been stress-relieved. Criterion barrels are all hand-lapped and are a good option for something less expensive than the custom makers turn out. A Kreiger will cost you an extra $70, but are cut rifled and hand-lapped and are a mainstay among match shooters. The lapped finish is finer in the Krieger I own than in the Criterion barrels I've bought. The Criterions get the Iosso/Flitz treatment from me, and I usually touch my crowns up slightly, but that's me being compulsive and not because I have any scientific evidence that it's necessary. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

May 23, 2015, 08:37 PM	#55
Road_Clam Senior Member Join Date: November 21, 2013 Location: New Hampshire Posts: 1,695	Uncle Nick, I'm confused at what your stating , why did you take my 24" bbl avg velocity and multiply it by .91 ? Do my numbers seem off ? __________________ "To be old an wise you must have been young and stupid"

May 23, 2015, 10:25 PM	#56
Metal god Senior Member Join Date: April 10, 2012 Location: San Diego CA Posts: 6,876	If I may Unclenick ? He was patting him self on the back His calculations say if you have an ave muzzle velocity of 3360fps from a 24" barrel as you do . When you shoot that same ammo from a 16" barrel you should get an ave of 3058fps . Seeing how your results show an ave MV of 3077fps from a 16" barrel . His formula is pretty accurate because it's not only inside your ES it's inside your SD . That is a pretty good formula if you ask me . __________________ If Jesus had a gun , he'd probably still be alive ! I almost always write my posts regardless of content in a jovial manor and intent . If that's not how you took it , please try again .

June 9, 2015, 01:14 AM	#58
Metal god Senior Member Join Date: April 10, 2012 Location: San Diego CA Posts: 6,876	Went and shot my 16" 1-9 twist AR using Fed GMM 77gr and some of my 77gr smk reloads . I only shot to 300yds . The 1-9 had NO problem stabilizing them out to 300yds . It was very windy in the afternoon and I did not have my rifle fully zeroed so there was no real group per-say but I did have all 20 shots make little tiny perfect cicles in the paper . myth further busted . __________________ If Jesus had a gun , he'd probably still be alive ! I almost always write my posts regardless of content in a jovial manor and intent . If that's not how you took it , please try again .

June 9, 2015, 09:19 AM	#60
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,063	Oley, Yes. My brain wandered and twisted down the path. Nothing new. M.G., Glad to see another 1 in 9 shooting these things. It's a funny business that some have problems and some don't. Awhile back someone published something on rifling twist tolerances and they weren't all dead on. It would be interesting to learn if some 1:9's are actually 1:9.5 or some are actually 1:8.7 or some such thing. Otherwise, it's different factors that account for the different results and it will take some work to sort them out. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

June 11, 2015, 03:18 PM	#61
Metal god Senior Member Join Date: April 10, 2012 Location: San Diego CA Posts: 6,876	When I cleaned my 1-9 I went ahead and checked the twist rate . It appears mine is just over 1-9 . I measured a 9" space on my cleaning rod . When the first mark reached the receiver I marked the top of the back line . I then pushed the cleaning rod in until the back line was at the receiver . The mark on the top line did not quite make it all the way around . It was very close but not straight up on top . It needed about 3/32 more to go . Not sure what that would translate to or if there is that much fudge room in that method . __________________ If Jesus had a gun , he'd probably still be alive ! I almost always write my posts regardless of content in a jovial manor and intent . If that's not how you took it , please try again .