Cronographed my 260imp 30 degree ??

[BradY]

Daj

I have the long throat reamer. With this, the junction of the boat tail is right on the same junction of the neck/shoulder plus or minus a bit depending on VLD or hybrids being used. Still plenty more room for powder and have shot up to 45gr 2209 (H4350). Im using 308 palma cases necked down and turned and CCI450's. My barrel is 30 inches (a maddco) so im thinking I wont be far behind you in velocity with the 43.8gr load. Yes vertical is very impressive indeed. I think there will probably be another node just above 45gr in my rifle, but I dont see the need to run it if this is shooting so well. If you compare ballistics on JBM with a 284W with 168 VLD's its almost identical to the 260imp running the 140 hybrids in the current node. If I want anything more in performance, really will have to go to a 7mm magnum and I dont think that will happen for a while yet (I dont really appreciate recoil)

I actually shot on sunday with 2x 15 shot strings, only dropped one point 3rd last shot of the day as my rifle came off the front rest. It was a 5 at about 7 oclock and probably only needed two bullet holes higher and it would have been a 6. Never mind, that shows me that I need to keep working on technique. I would love to have a MS2 here to chrony it, but now its going to be about a month so will wait patiently.

Barrel life is still going to be interesting but if I can get 1500 rounds of accurate life (still plenty of room in the neck to chase rifling) then I will be happy. Have enough meat on this barrel to last a good 3+ chamberings.

 

[Raptor]

daj,
Mine is short throated to load from the AI mag. I am thinking, but will check for sure, that my 139s are at 3.295OAL with the bullet compairator. By eyeballing it, it looks like the base of the bullet is about at the neck shoulder junction. (Not the boattail part)

 

[22BRGUY]

Wondering if I could ask what the case capacity of this 260 30 degree case is guys?

thanks

 

[Raptor]

Not sure what the H2O capicty would be but the case is .065 longer. I have no idea why this case produces the velocities that it does without showing pressure signs. I am sure I could push the 123s well into the hihg 3100s maybe even low 3200s and the 139s would go 2950+. I have already pushed the 139s to 2950 with no pressure signs. I am not going to go there because I don't want to ruin my brass or shorten its life.

My thoughts are to push the 139s to 2900 and maybe the 123s to 3000+. I did some long range load testing last night at 400 and 600 to see what I got for vertical on a few loads and had a couple at 600yds that shot in the 1.5" range for vertical. One load had a "0" vertical at 400yds. Unfortunatly I do need to do more testing because the load the shot good at 400 was so so at 600 and the load that shot good at 600 was so so at 400 but it wasn't the greatest night for testing with switching winds from half to full value.

 

[daj]

22BRGUY, my 260Imp30 case capacity is 55.1gr H2O.

 

[22BRGUY]

Thanks much daj...I noticed that that is very close to the 6.5 SLR cartridge as seen on 6mmar.com. Loads and performance should be very close to each other I would think.

 

[Raptor]

I believe the 6.5SLR keeps the same case cap. as the stock case.

 

[Raptor]

I have been doing some longrange load testing and thought I had a great load at 44 to 44.2grs of H4350 with the 139s but what I found out was I now have about 70 to 80rds of Lapua brass with very loose primer pockets!!

I am just sick over this because I had no real pressure signs and from what I can tell this should not be all that hot of a load. I was getting just a bit of a primer pitting at 44.2 so decieded to stay at 44grs and I was getting .5moa groups at 600yds with it shooting off the hood of my pickup.

I had no stiff bolt lift or ejector marks on the cases. THe one thing I did notice was when I firefomed the new brass I used 43grs of H4350 with the 140s and when I reloaded these cases for the first time as a formed case I noticed that the primer didn't go in as hard as ususal for the Lapua cases. Usually with new Lapua brass the first several loadings the primers are usually a pretty snug fit. Not so this time.

Could my fireforming load be to hot?? Just wondering what you guys are using?? Thanks!!

 

[BradY]

Im staying with 43.7gr H4350 with 140 hybrids jumped 15 thou. The load absolutely hammers and vertical at 900yds is borderline unbelievable. I dont see why that would change at 1000yds. Havent had any loose primer pockets yet but Im using lapua palma cases necked down and turned. Absolutely fantastic.

 

[LongRanger]

Raptor...

I and 2 friends had some new cut rifled barrels melonited after firing a few rounds to establish some base-line speeds.

Our first rounds through the treated barrels were dramatically faster...way over pressure, in my case with a 7rsaum, 130 fps faster than my base-line with the same charge. It makes sense since you end up with a frosted-looking barrel inside and out that started out shiny.....the bore is, effectively, smaller and will stay smaller until is wears down through firing and/or a LOT of cleaning rod pushing and pulling.

I'm going to post some notes on our results at a later date.

The melonited surface is incredibly hard and you get only the one, initial chambering on your barrel. Nobody should expect to find a gunsmith willing to tear up his tools trying to set-back a melonited barrel. One smith told me he tried it ONCE and destroyed his cutting tools and reamer.

Frank B.

 

[texote]

This is a good read!

Has anyone tried 4831 sc, I've been told that is the powderr to use fOr the 260 ack 40°.

 

[Raptor]

Longranger thats intresting because mine is very fast for what I am loading. I was pushing 139s at close to 2950fps with what I "Thought" was a lighter load for this caliber. I even got a second cronograph because I didn't believe my readings.

When I got mine back I thought I would have to really scurb the barrel but it was as smooth as glass. I still polished it with a bronze brush and fine steel wool strands wraped in it just to be sure.

The barrel just does not foul even after a 120rounds through it it took two patches to come out clean with no blue on them.

 

[BradY]

Re chrony the load. Charles Ballard found that after a couple of hundred shots his 284 barrel gained speed and his loads went from fine to overpressure. He loaded back to the original velocity and set a record with it. This might have happened again in your case.

 

[Raptor]

1983,
My load of 43.6grs of H4350 with 140MKs shot 5 into 3"Hx2.5"V at 600yds. I am going to test it with 139s next because they tend to shoot better in my rifle.

I had a couple of loads of 123 Lapuas that shot as well and that is probably the bullet I will go with if I can get a load that will shoot as well as the 139 and 140s have been shooting.

I like my 6.5x55 for the heavier bullets and really liked the 123s in my last 260. If the damn wind ever quits blowing out here I will try to get back out and confirm some of these groups and them get some numbers on them. Thanks guys for all the replies and help!!

 

[BradY]

Just measured my throat too, in 350 rounds Ive had 3 thou erosion. This is with a softer brand barrel made here in Aus.

I reckon its a perfect cartridge for 140gr class bullets for target shooting. On paper at your measured velocities its very similar to 284W and 180gr bullets at 2800-2850fps which is realistic velocities for that combo. Im very sceptical of the 123 lapua BC figure I must admit but Im happy to be proved wrong. If you want to shoot lighter bullets I would favour the 130VLD. From shooting a 6.5x47L with the 130's against another with 123's my drift was better.

 

[Raptor]

1983,I sure don't doubt what your saying. I have heard really good things about the 130s. I have a bunch of the 123s and they did shoot really well in my last 260.

Like I said earlier I do have the 6.5x55 for the 139s and I also have a 284 which I love for long range shooting. This last weekend I was able to bang a 19"x26" plate 4 out of 5 times at 1343yds. We came back in the afternoon after we got rained out and tried it again in a 18 to 25mph cross wind and with 13MOAs of wind hit it again 3 out of 5 times. I was pretty happy with that.

The gun does seem to really like the 140s and 139s so I may stay with them because my 6.5x55 is getting a lot of rounds down the barrel. With the velocity that the 260imp 30 degree is shooting I am not sure I have a need for the 6.5x55. I built it to hopefully get more rounds out of it than the 260 by using a slower burning powders but the damn thing loved H4350. So I didn't really gain much with it.