260 Rem AI velocities

[Terry_M]

I filled a couple fired cases with water and weighed them on an RCBS digital scale. It measure 55gr water in Lapua and LC LR brass.

I was expecting 56 or 57 grains H2O capacity.

I adjusted QL to match what I weighed and it matches the velocity I'm getting over my Chrony and a Magneto Speed I borrowed from a friend.

I had the throat cut short so I could reach the lands with long bullets like A-Max or Berger VLD's.

Have you ever shot charges up until you see ejector marks on the case head? Preferably using H4350??

I did. Ejector marks and flattened primers started at 44gr, and that's where I stopped.

At that 44gr area was the ejector marks bad enough that you saw them on 3 out of 5 rounds??

3 for 3 had ejector marks.

QL shows me being at 60,233 ft lbs pressure. 55gr case capacity, 26" barrel, 2.835COL, 103% CF, 6.5mm-08 is the cartridge I chose to work with in QL since 260AI was not an option.

 

[Terry_M]

This is the first rifle I've ever worked on velocity with an anticipated goal in mind from the outset. I want to hit 3000fps with a good stable *safe* load. Something that can preserve brass life, but if I only get 5-6 loadings I'll be happy. I know 2900 - 2950fps is more realistic.

Typically I would plug different powders into QL and then start 10% low and move up .3 - .4 grains at a time with 3 shot groups to see which performed best at 200yds. Then load up ten of the rounds that shot the best and get chrono numbers, by shooting 2-5 shot groups, at 100yds, over the chrony.

I guess my next option is to pull the barrel off and put it on a long action so I can have it throated out until the bullets can be loaded above the case neck junction and cram as much powder as possible in the case. That is if the 7828 and or 7977 don't deliver what I'm after.

I've heard that the spacer can be removed from the AI mags to allow for longer bullet seating. Have any of you done this? Is the gain worth modifying the mags?

If your serious about reworking the throat you may want to try this chamber I have here.. It basically looks like a Dasher neck/shoulder area.. The shoulder is 40 degrees... But the shoulder looks shorter than a AI case.. My shoulder is just .136 tall.. The 6.5 neck is .200 tall... Just go over to the 6mm Dasher Ultra Mag thread and look at them measurments.. They came off a 308 Palma case sized to this Improved 260 cartridge.. I'm going to try it in a 6mm... If yall are interested I can measure its water capacity maybe or just feel it up with H4350 for us to see what it will hold... I think it will get your 3,000fps with 140gr bullets...

Thank you, I will check it out.

I have a few hundred 260 Lapua brass and was thinking of selling/trading them for 308 Palma brass to see if the smaller primer would help with pressure, but I'm not sure it will since the pressure signs are ejector marks, not punctured primers. They are flattening, but I have not run a load hard enough to fully flatten them.....yet

 

[SDDasher]

The 260ai is one of those cases like a 308ai that just dont improve as much as the trouble to do it. Now a 250sav ai and a 22-250ai are definitely worth it.

Dusty, I may be the exception to improving the parent case 260 to an improved case. I have owned two previous 260's and could never get them to tune to match (F-Class m/r-l/r) expectations of High Master scores consistently.
Since going to the improved case not only have my scores become more consistent, they have increased on average. That is why I decided to re chamber my .308 hunting rig to the 260 AI. As you know I primarily shoot the Dasher, but I am quickly becoming a 40* shoulder 260 AI fan.

 

[wboggs]

Terry_M What length throat do you have now? Thanks Bill

 

[SHootSTraight22]

I guess what bothers me regarding your whole situation is I shoot a 6.5x47 at 2,800fps with 40gr H4350 and have another load at 41.7gr at 2,900fps "plus I'm sure..." I start showing "a few" ejector marks around 41.8-42gr area but nothing dangerous.. Now, with that info plug it in to your QL and see what you get.. You maybe able to take that info from QL and estimate what you would gain by shooting Palma brass with your 260AI... I really would like to see you run these figures and post.. Please???

 

[Toolbreaker]

I wonder what your velocity would look like with VV N560?

 

[STOMP442]

I am running 42.0 grains of H4350 in my 260AI and I am getting 2940fps out of a Mcgowen 26" tube. Accuracy is phenomenal at this node. Anything higher opened up the groups.

 

[coyotekiller82]

I'm running 140gr Berger Hybrids @2900fps out of my 260AI ballistics run the same as my FF loads with 123gr SMKs. This velocity is what I was going for from the get-go, plenty accurate & easy enough on my brass, which is Remington brand (keeping the pressure down should help keep the primer pockets from stretching). I may switch up to Lapua brass some day, but not until my Rem brass starts to deteriorate.

 

[Terry_M]

Terry_M What length throat do you have now? Thanks Bill

I'll talk to the gunsmith tomorrow and get the numbers off the print. I know I reach the lands @ 2.650 COL with a Berger 140 VLD. 2.865 is where I hit the lands. I apologize for the mis-type.

 

[Terry_M]

I wonder what your velocity would look like with VV N560?

QL shows 48gr as 107% CF and 2973 FPS , so worth a try.

 

[Terry_M]

I am running 42.0 grains of H4350 in my 260AI and I am getting 2940fps out of a Mcgowen 26" tube. Accuracy is phenomenal at this node. Anything higher opened up the groups.

Can you please provide specifics of your load? Brass, primer, COL (distance from lands), and any other small details you can think of.

I'm genuinely interested in figuring out how you can achieve such velocity, and curious if I can find a way to replicate your results.

Thanks in advance.

 

[Rockfish Dave]

I am running 42.0 grains of H4350 in my 260AI and I am getting 2940fps out of a Mcgowen 26" tube. Accuracy is phenomenal at this node. Anything higher opened up the groups.

Can you please provide specifics of your load? Brass, primer, COL (distance from lands), and any other small details you can think of.

I'm genuinely interested in figuring out how you can achieve such velocity, and curious if I can find a way to replicate your results.

Thanks in advance.

I'm intrigued as well. That you are getting higher velocity, with less powder in a larger volume case than I am with more powder and smaller volume case. Seems impossible, and yet here you are. Are you shooting 120gr projectiles?

 

[wboggs]

Terry_M
I would think that reaching the lands at 2.65" with the 140 VLD is putting much of your bullet in the case and severely limiting the amount of a slow burning powder you can load.
Bill

 

[STOMP442]

Blows my mind as well, I even checked through two different chronys which resulted in only 7fps difference between the two. Only thing I can figure is that I have a little bit of a tight chamber and a fast barrel.

Lapua Brass
140gr Berger VLD .025" off the lands which gives me a C.B.T.O. of 2.120"
CCI LR # 200 primers

I had a criterion barrel prior to this one that required 44.0gr of H4350 to get to the same velocity node.

 

[wboggs]

STOMP442 Since the nose of a 140H is 0.721, you are probably at 2.816 OAL if you are 0.025 off. That 2.65 puts a lot of the bullet in the case.

 

[SHootSTraight22]

STOMP442 Since the nose of a 140H is 0.721, you are probably at 2.816 OAL if you are 0.025 off. That 2.65 puts a lot of the bullet in the case.

With your example just giving and my 260AI case/and 140H bullet that would be the whole service area of the boat tail hanging around in the "body area.." A good .225 of boattail!!!

 

[taliv]

i ran my 260AI with R17 at 3047fps for a while but brass didn't last too long. i dropped it back to 3000 fps and probably shot about 3 years of matches at that velocity. after 1500 rounds or so that 3000 will have fallen to 2950 or so. i just keep adding powder to maintain 3000ish. At 3000 fps, i can switch back and forth between R17 and H4350 depending on what i can find in stock, with no change in accuracy, though obviously the charges are different.

pretty much all of the above involve ejector marks, but not flat primers.

currently, for no good reason, i'm running super light at 2810 fps.

 

[wboggs]

Are you getting comparable accuracy with R17 and H4350?

 

[taliv]

yes, accuracy is the same to me, but i don't shoot benchrest. anything under .5 MOA is "good enough" for me, maybe not for others.

only real difference in those powders is one's faster, 3x the temp sensitivity, and they only put 5 lbs in a 8 lb jug. (uhh, hello?)

 

[STOMP442]

STOMP442 Since the nose of a 140H is 0.721, you are probably at 2.816 OAL if you are 0.025 off. That 2.65 puts a lot of the bullet in the case.

There is a lot of bullet in the case and I like it that way. This gives me a lot of room to chase the lands with and I can't argue with the accuracy or the velocity I am able to achieve with this barrel. I am going to cry like a little girl when it comes time to replace it, but hopefully that's quite a few years down the road.