Accuracy International .260
- Thread starter mercracing
- Start date
Basically the point of this is for anyone with problems or insight to chime in.
I am shooting an AI AXMC in 260. NF 7-35 in a Spuhr. I just spun on a new 24” 260 barrel I bought from MH. SiCo Harvester on the end.
I shot 100 rounds through it and wanted to start shooting groups and checking speed. FGMM shot great for me before so I tried that, Hornady, and Berger factory loads. All shot like garbage. 1.5-2” outside to outside. I went home and took the barrel off, reinstalled and retorqued, and cleaned. Checked scope mounts also. I went out last night with only FGMM. I shot three to foul then two 5 shot groups and one 10 round string for ES/SD. The two groups looked to be a little under an inch, I forgot to measure. The 10 shot string was ok speed wise, but not awesome for ES/SD. I’m hoping to have the Berger ammo by the weekend so I can test those then.
I am shooting an AI AXMC in 260. NF 7-35 in a Spuhr. I just spun on a new 24” 260 barrel I bought from MH. SiCo Harvester on the end.
I shot 100 rounds through it and wanted to start shooting groups and checking speed. FGMM shot great for me before so I tried that, Hornady, and Berger factory loads. All shot like garbage. 1.5-2” outside to outside. I went home and took the barrel off, reinstalled and retorqued, and cleaned. Checked scope mounts also. I went out last night with only FGMM. I shot three to foul then two 5 shot groups and one 10 round string for ES/SD. The two groups looked to be a little under an inch, I forgot to measure. The 10 shot string was ok speed wise, but not awesome for ES/SD. I’m hoping to have the Berger ammo by the weekend so I can test those then.
So, we know there are three of us having issues with factory loads with our AI .260's.
Mine is a factory AT that came in .308. I replaced the .308 barrel (unfired) with a 24" threaded AI .260 barrel in FDE. I installed a SOCOM 7.62-RC brake and was using a SOCOM suppressor. I was getting inconsistent groupings across a variety of factory ammo, including:
Prime 130gr
Hornady ELD-M 130gr
Berger 130gr
Berger 136gr
Berger 140gr
Black Hills 139gr
McCourt 130gr and
FGMM 142gr
The Prime and Hornady showed the best groupings.
I thought it could be the brake so I removed it, did a clean and inspect and removed and reinstalled the barrel. I went back out and the first 3-shots with the Prime (including a CCB) were basically in the same hole at 100 yards. The Hornady was 1/2 MOA and the Bergers were all at 1MOA or higher.
Prime 3-shots after I cleaned and reinstalled the barrel. It still needs to speed up and only had about 100rds at the time:
Groups with the other loads and the surefire brake:
Other groups with the Bergers and FGMM:
The Prime and Hornady after removing the brake and reinstalling the barrel:
Just to mention, I've been shooting a Mausingfield M5 with a Kreiger 5R in .260 for a couple of years. While it prefers the Hornady, other rounds do show a POI shift and open up the goups a bit, but not like this AI barrel.
I intend to do some chamber measurements, along with factory COAL and BTO to try and narrow the issue. I know it was close to liking the Hornady at 2.820 (COAL) but it did not like the Hornady at 2.780, which tells me the chamber may be long and with a preference towards a longer BTO.
I'll update the thread once I get some additional data.
Mine is a factory AT that came in .308. I replaced the .308 barrel (unfired) with a 24" threaded AI .260 barrel in FDE. I installed a SOCOM 7.62-RC brake and was using a SOCOM suppressor. I was getting inconsistent groupings across a variety of factory ammo, including:
Prime 130gr
Hornady ELD-M 130gr
Berger 130gr
Berger 136gr
Berger 140gr
Black Hills 139gr
McCourt 130gr and
FGMM 142gr
The Prime and Hornady showed the best groupings.
I thought it could be the brake so I removed it, did a clean and inspect and removed and reinstalled the barrel. I went back out and the first 3-shots with the Prime (including a CCB) were basically in the same hole at 100 yards. The Hornady was 1/2 MOA and the Bergers were all at 1MOA or higher.
Prime 3-shots after I cleaned and reinstalled the barrel. It still needs to speed up and only had about 100rds at the time:
Groups with the other loads and the surefire brake:
Other groups with the Bergers and FGMM:
The Prime and Hornady after removing the brake and reinstalling the barrel:
Just to mention, I've been shooting a Mausingfield M5 with a Kreiger 5R in .260 for a couple of years. While it prefers the Hornady, other rounds do show a POI shift and open up the goups a bit, but not like this AI barrel.
I intend to do some chamber measurements, along with factory COAL and BTO to try and narrow the issue. I know it was close to liking the Hornady at 2.820 (COAL) but it did not like the Hornady at 2.780, which tells me the chamber may be long and with a preference towards a longer BTO.
I'll update the thread once I get some additional data.
Last edited:
ill look for some pics but i tried 3 boxes of each copper creek (with lapua brass):
mile high gradious 260 barrel
berger
scenar
SMK
berger shot like pics above (sold the remainder to some on the hide a few months ago)
scenar shot the best/very good. 1/2 moa
SMK was acceptable .5-.75 moa
mile high gradious 260 barrel
berger
scenar
SMK
berger shot like pics above (sold the remainder to some on the hide a few months ago)
scenar shot the best/very good. 1/2 moa
SMK was acceptable .5-.75 moa
I've only shot a couple of boxes of factory ammo and had no joy. Is reloading out of the question for you guys?
By reloading my .260 shoots everything well, 107s, 123s, 140s, it really doesn't care. Here's a load for 123gr that is consistently one hole at 100yds. Use it at your own risk.
123 gr Hornady ELD Match
Federal 210M Primer
Lapua Brass
39.3 grs Varget
22" Bartlein 5r barreled & suppressed AIAT
2894fps 2.4 SD
5 shots one hole .264
By reloading my .260 shoots everything well, 107s, 123s, 140s, it really doesn't care. Here's a load for 123gr that is consistently one hole at 100yds. Use it at your own risk.
123 gr Hornady ELD Match
Federal 210M Primer
Lapua Brass
39.3 grs Varget
22" Bartlein 5r barreled & suppressed AIAT
2894fps 2.4 SD
5 shots one hole .264
I CAN reload, but I enjoy my free time. In a perfect world I’ll find a factory load that works. Second plan is to find something to finish the year with and reload a bunch over the winter so I have about 1k in stock to compete with next year. No, 1k won’t last me the year, but it’ll be a good start.
260 is OG cool. If you know, you know.
I'll be ordering a short for caliber barrel for the ASR once MH or EO can confirm the barrel tenon specs (in the event it differs from the AXMC).
I'll be ordering a short for caliber barrel for the ASR once MH or EO can confirm the barrel tenon specs (in the event it differs from the AXMC).
I can reload also, but with the world's best sniper rifles, I don't think that should be a requirement. The chamber should be reamed to a spec, we just need to find out what that spec is and find a factory load that is close.
I don't see where others are having to do the same to get their calibers shooting, so I wonder if the .260 reamer spec is a bit off or if they used a differing profile????
From LRIs barrel fitting section, this is what they can ream to. For example, if you tell them you will be shooting FGMM, then they will select the closest and ream the barrel to shoot the FGMM.
I don't see where others are having to do the same to get their calibers shooting, so I wonder if the .260 reamer spec is a bit off or if they used a differing profile????
From LRIs barrel fitting section, this is what they can ream to. For example, if you tell them you will be shooting FGMM, then they will select the closest and ream the barrel to shoot the FGMM.
| 260 REMINGTON MATCH-TAC | 0.296 | 1.5* | 0.18 |
| 260 REMINGTON MATCH | 0.296 | 1.5* | 0.095 |
| 260 REMINGTON MATCH | 0.296 | 1.5* | 0.096 |
| 260 REMINGTON MATCH | 0.2955 | 1.5* | 0.095 |
| 260 REMINGTON TAC MATCH | 0.297 | 1.5* | 0.056 |
| 260 REMINGTON ACKLEY IMPROVED | 0.298 | 1.5* | 0.055 |
i too am chasing a load in an AI chambered 260. in fairness to the barrel i am just getting started.
its been one of those barrels where everything seems to stack up against you. but im just getting started so not giving up.
24” 2018 profile AI original to gun, that had to be cut down to 20.
when initially working up loads i found that i could only load out to a base to ogive of around 2.155. this was measured with dummy rounds seated progressively lower till bolt closed. seemed ‘short to me’. initially i tried to chamber a dummy round for a load for a different gun thats seated farther, but that turned into a rubber mallet mess to get it out.
ive put about 50 rounds through it now of 142 smk, gathering speed data. one days tests are below. not as bad as some other posters but not where it needs to be.
along the way i ordered a new 24” ai 260 barrel to replace the original 24”. havent shot it yet, but i did test size rounds to see what lengths i could get in it and low and behold its longer than the 20”.
knowing i put some rounds now through the 20” i went and checked and sure enough i can now chamber longer seated bullets. not much longer but longer. base to ogive on my next set of test rounds now sits at around 2.225 base to ogive. i wouldnt expect the throat to erode that quickly . . . but maybe it can. or maybe LRI complimentsrily cleaned it up when they were shortening it ?
anyhow ive got some loads set up to try to find a node on next trip seated at longer lengths. may be a while but will report back what i come up with. will find a node and then play with seating depth.
following is test page of two shots at each test load. (ignore 300 win mag group on bottom right). i wouldnt call 2 rounds a group, but multiple sets of 2 round shots start. to denote a pattern.
had some real wonky results. as i went up in powder at one point i actually had impacts move downward, then back up at next higher charge. hadnt seen that before. shot from prone off bipod. i will admit the ai trigger is new to me. im a lifelong singlstage ascribor. shots went from third row left to right to second row left to right.
its been one of those barrels where everything seems to stack up against you. but im just getting started so not giving up.
24” 2018 profile AI original to gun, that had to be cut down to 20.
when initially working up loads i found that i could only load out to a base to ogive of around 2.155. this was measured with dummy rounds seated progressively lower till bolt closed. seemed ‘short to me’. initially i tried to chamber a dummy round for a load for a different gun thats seated farther, but that turned into a rubber mallet mess to get it out.
ive put about 50 rounds through it now of 142 smk, gathering speed data. one days tests are below. not as bad as some other posters but not where it needs to be.
along the way i ordered a new 24” ai 260 barrel to replace the original 24”. havent shot it yet, but i did test size rounds to see what lengths i could get in it and low and behold its longer than the 20”.
knowing i put some rounds now through the 20” i went and checked and sure enough i can now chamber longer seated bullets. not much longer but longer. base to ogive on my next set of test rounds now sits at around 2.225 base to ogive. i wouldnt expect the throat to erode that quickly . . . but maybe it can. or maybe LRI complimentsrily cleaned it up when they were shortening it ?
anyhow ive got some loads set up to try to find a node on next trip seated at longer lengths. may be a while but will report back what i come up with. will find a node and then play with seating depth.
following is test page of two shots at each test load. (ignore 300 win mag group on bottom right). i wouldnt call 2 rounds a group, but multiple sets of 2 round shots start. to denote a pattern.
had some real wonky results. as i went up in powder at one point i actually had impacts move downward, then back up at next higher charge. hadnt seen that before. shot from prone off bipod. i will admit the ai trigger is new to me. im a lifelong singlstage ascribor. shots went from third row left to right to second row left to right.
Attachments
I got my AXSA used in 308 from Mile High in Feb this year. They had a NOS Tooley-spun 260 barrel (Bartlein 1:8", 24" long and 5/8-24 threads) on the shelf, so I snagged it also. Put a Hellfire on it and first shots with Prime 130 .. yeah, I suck and strung it horizontal:
It doesn't shoot the FGMM 142 (2740fps) as well as the Prime (2860fps):
So far, no issues with my loads in it either. Here's 10rds of 139 Scenars over 42.8gr H4350 at 200 (2800fps). Measures 2/3moa:
It doesn't shoot the FGMM 142 (2740fps) as well as the Prime (2860fps):
So far, no issues with my loads in it either. Here's 10rds of 139 Scenars over 42.8gr H4350 at 200 (2800fps). Measures 2/3moa:
Last edited:
Using the Stoney Point, my BTO for the barrel and Lapua 139s is 2.358".
I load them to 2.275" BTO (2.835" OAL)
I also shot a box of the Hornady 130ELDM. Best group was .51moa, worst was .73 at 200yds. Magnetospeed said 2785fps.
Best:
Best:
I called MHS and they don't have any .260 barrels in stock. They could spin one up, but 6-8 weeks.
I measured the COAL and BTO of 10 rounds from each of the ammo types I was shooting:
The key is the BTO. My rifle liked the Prime and the Hornady +2. The Prime is at 2.1810 and the H130s are at 2.1800, whereas the Bergers were longer. This is telling me there is not much jump to the lands and maybe the chamber was finished short. I need to do more measurements and see if I can slug the chamber somehow. It's interesting that the FGMM is hovering around 2.1825 but it did not shoot well from my barrel.
The Prime was moving at 2907fps and the H130s were at 2800fps. I think the barrel will speed up a bit once I get more rounds out.
I measured the COAL and BTO of 10 rounds from each of the ammo types I was shooting:
The key is the BTO. My rifle liked the Prime and the Hornady +2. The Prime is at 2.1810 and the H130s are at 2.1800, whereas the Bergers were longer. This is telling me there is not much jump to the lands and maybe the chamber was finished short. I need to do more measurements and see if I can slug the chamber somehow. It's interesting that the FGMM is hovering around 2.1825 but it did not shoot well from my barrel.
The Prime was moving at 2907fps and the H130s were at 2800fps. I think the barrel will speed up a bit once I get more rounds out.
I called MHS and they don't have any .260 barrels in stock. They could spin one up, but 6-8 weeks.
I measured the COAL and BTO of 10 rounds from each of the ammo types I was shooting:
The key is the BTO. My rifle liked the Prime and the Hornady +2. The Prime is at 2.1810 and the H130s are at 2.1800, whereas the Bergers were longer. This is telling me there is not much jump to the lands and maybe the chamber was finished short. I need to do more measurements and see if I can slug the chamber somehow. It's interesting that the FGMM is hovering around 2.1825 but it did not shoot well from my barrel.
The Prime was moving at 2907fps and the H130s were at 2800fps. I think the barrel will speed up a bit once I get more rounds out.
You may want to look more at the type of ogive as much as the BTO. The gov't specs SMKs for their OTM match and sniper ammo because they are proven to be more tolerant of different jumps. Their spec for MK248 Mod 1 requires a BTO length to be held within 0.005". They don't specify the length, but specify the consistency in length. I am surprised the 142 FGMM doesn't perform as well in either of our rifles, but look at the BTO spread ... Hmmmmm? Even the Prime has a big spread, but it PERFORMS. Above my paygrade, I guess.
Appreciate the reply; I'm tracking. There are so many variables all the way down to the amount of bearing surface. I'm also wondering why that FGMM didn't perform and my first thought was the SMKs BTHP design. I'm going to have to search a bit to see what jump an AI .260 may prefer. I've only found one thread so far and it said 0.030, but that's a single data point and not verified.
Most of the time a SMK will be comfortable jumping at least 0.020". Gov M852 (308) was loaded at 2.244" BTO (2.815-2.820 COAL) for magazine feeding in M14s. While it was really made for 300m shooting in CISM, it shot across the NM course very well. I shot 196-198 at 500yds in my M14 frequently. I believe those bullets were jumping about .060-.120, depending on barrel life.
As measured, the 142SMKs were jumping 0.176 in my barrel! My 260 R700 has a 25" Bartlein 1:8" and shoots the FGMM 142s quite well and they jump 0.098".
I experimented and pulled 10rds of the Hornady 130s and reseated them to a .030" jump. I had no appreciable accuracy change at 200yds and lost 20fps.
Based on all the bullets I have measured, my throat is a little long. I get BTO of 2.320" (136L) - 2.375" (142SMK). If I load 147ELDMs or 130TMKs I cannot get under a 0.025" jump without using AW mags as mine allow .010" more than my AX mags.
FGMM 142smk jumps well over a tenth of an inch in my 260 and shoot amazingly!
At 300 yards
I haven’t met a SMK yet that doesn’t like jump.
I asked Proof what spec they use for their carbon fiber .260 barrels. They replied quickly and while they wouldn't divulge their exact specs, they did refer me to the SAAMI reamer specs and said their neck is just a tiny bit tighter and the freebore a little shorter than standard SAAMI.
Link to the 375 page SAAMI Approved Industry Performance Standards in case you don't already have a copy, 260 is on page 81.
Link to the 375 page SAAMI Approved Industry Performance Standards in case you don't already have a copy, 260 is on page 81.
I just ordered a Proof Research Carbon Fiber 24" in .260. I ordered through ExpertVoice and got the 30% Mil discount. The Proof folks said they build these to order and are running three shifts trying to catch up with the demand so, it could be a bit before I receive the barrel.
I also sent a note to Dave Tooley.
I also sent a note to Dave Tooley.
McCourt ammo you used, was it loaded for LaRue gas gun or did you get ammo geared for a bolt gun / AI 260 bbl?
Two very different loads for two very different platforms.
Received a shipping notice from Proof and the carbon fiber barrel should be here Friday the 7th.
Also measuring some 1x fired cases, and sent some Prime and Lapua 1x fired cases to Hornady for them to drill and thread for my LnL OAL comparator.
Also measuring some 1x fired cases, and sent some Prime and Lapua 1x fired cases to Hornady for them to drill and thread for my LnL OAL comparator.
I like the 130gr ELD-M, the 130gr Norma Golden Target and the 139gr Lapua Scenar. That's me, not necessarily my barrel. 
That's good news. I ordered a Proof barrel so I'm going to stand down and shoot the .260 gasser tomorrow at Quantico. I'll have the Proof next Friday, will do some measurements and see if I can get it zeroed Saturday for long range Sunday. I know, first world problems.
The Prime I have is shooting well in this barrel BTW.
The Prime I have is shooting well in this barrel BTW.
Made it out Saturday and Sunday. Saturday tried the Berger 140 ammo again. Better numbers and an ok group. Went to go make a bulk order... out of stock tried Prime and FGMM again. Prime was meh. GMM was garbage still. I made a call this morning and was able to get a place to order me 1k of the Berger ammo. I’m going to clean this barrel and my old one over lunch and shoot some GMM after work and see if I can get something to work for the weekend.
tried Prime and FGMM again. Prime was meh. GMM was garbage still. I made a call this morning and was able to get a place to order me 1k of the Berger ammo. I’m going to clean this barrel and my old one over lunch and shoot some GMM after work and see if I can get something to work for the weekend.
Made it out Saturday and Sunday. Saturday tried the Berger 140 ammo again. Better numbers and an ok group. Went to go make a bulk order... out of stock
Can you measure the OD of your fired cases? My fired brass is measuring an OD of 0.2985. My intent is to try and narrow down the chamber dimensions, even though I know different companies cut these barrels.
Sorry, I didn’t get a chance to measure yesterday. I’ll try today.
So yesterday I went home over lunch and cleaned my old and new 260 barrel. Went to the range last night and shot 8 groups. I shot 6 out of the new barrel, two groups of three different ammo. I used FGMM, Berger, and ELDM factory ammo. None shot what I would call great. I took off the new barrel and put on the old barrel and shot two groups with FGMM. The two groups out of the old barrel are, to me, decently better then new barrel.
So yesterday I went home over lunch and cleaned my old and new 260 barrel. Went to the range last night and shot 8 groups. I shot 6 out of the new barrel, two groups of three different ammo. I used FGMM, Berger, and ELDM factory ammo. None shot what I would call great. I took off the new barrel and put on the old barrel and shot two groups with FGMM. The two groups out of the old barrel are, to me, decently better then new barrel.
@Defender3 i assume you were measuring the neck. Once fired Berger factory ammo(Lapua brass) measures .2995. I only checked two pieces.
I took the .260 Proof CF barrel to the range to see how it shoots. I tried a variety of factory ammo but damn if I didn't forget my legacy Prime. I may go back out tomorrow to give it a try. The barrel shot well and I was surprised that it shot FGMM so well, maybe it was the design of that Sierra bullet, who knows. It also really liked the factory Berger 136gr Lapua Scenar. I may do some measurements and see how each of those were in relation to the lands. I also shot it using a Sandman-L, which required a full 0.7mils up.
Interesting was that the Night Force was zeroed and sighted for 6.5CM. I took the 6.5 barrel off and put the proof on and it was right at teh 6.5CM zero. Just an interesting tidbit given these calibers are so similar.
One the range:
The temp strip was working well. I fired string and then used the magnetospeed rifle kuhl to drop the temp back down to 95 degrees. This temp was after a 6-shot string on a 78 degree day.
The results, I should have done better but I was rushed to see my wife off to of all things, Yoga Camp.
Interesting was that the Night Force was zeroed and sighted for 6.5CM. I took the 6.5 barrel off and put the proof on and it was right at teh 6.5CM zero. Just an interesting tidbit given these calibers are so similar.
One the range:
The temp strip was working well. I fired string and then used the magnetospeed rifle kuhl to drop the temp back down to 95 degrees. This temp was after a 6-shot string on a 78 degree day.
The results, I should have done better but I was rushed to see my wife off to of all things, Yoga Camp.
Similar threads
