.260 in aics mag. can you reach the rifling?

[maccrazy2]

I will call ptg tomorow but I wanted to get some feedback here also. I called Dave at ptg and had a .260 no neck turn match reamer made for 142gr smk bullets to be used in a kregier 5R barrel. I let dave know I wanted to be able to reach the rifling and have the rounds fit in an AICS mag (mine measures 2.895) I just got the barreled action back from the smith this weekend and reassembled everything. I started setting up for loading some load work up rounds. Lapua 260 brass and 142smk. I seated a bullet slightly long and used the bolt to seat it to the lands to get the max oal legenth. It is 2.955 oal. So, I will have at least .070 jump assuming only .010 clearence for the round in the mag which is tighter than I prefer.
I just had the rifle rebarreled from .308 and have not owned a 260 before. Can you guys reach the rifling with mag legenth rounds? When I spoke with Dave I said I wanted to be able to do that and he said it was no problem. However it is not the case now. I did get a go gauge made with the reamer and the fit is correct so incorrect headspace is not an issue.

 

[maccrazy2]

Re: .260 in aics mag. can you reach the rifling?

I also made sure the bullet was not sticking in the rifling and creating a false OAL reading.

 

[AtownBcat]

Re: .260 in aics mag. can you reach the rifling?

I have a 6.5x47 and I not sure how close the cases are(but im posting this because they are always compared so I figured they have to be in the same ball park) I am .005 in the lands and I have plenty of room in the aics mag. Not even close...hopefully this helps.

 

[Boomholzer]

Re: .260 in aics mag. can you reach the rifling?

What was your O-give length and seating tolerance to approach lands in the prior .308? Not sure what your expectations are from coal to o-give also in a mag-fed rifle.
2.88+ coal is aggressive in AICS mags.
You referenced coal in mag against tight throat to bore. Post observance is also coal. O-give reference is only to 142SMK as a bullet without associated seating depth.

Not sure what you were expecting given the stated.

edited to add; your better off where it's at now.

 

[maccrazy2]

Re: .260 in aics mag. can you reach the rifling?

Prior barrel was a factory tactical remington barrel. I will have to reference my notes to see what the jump was on it but that was why i specified a specific bullet and i wanted to be able to touch the rifling using mag fed rounds.
Dave recommended a specific throat angle in a match reamer and i deferred to his judgement. Maybe that changed things. I will find out tomorrow when i call.
I was just under the impression what i asked for was common and not a problem at all.

 

[maccrazy2]

Re: .260 in aics mag. can you reach the rifling?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Boomholzer</div><div class="ubbcode-body">What was your O-give length and seating tolerance to approach lands in the prior .308? Not sure what your expectations are from coal to o-give also in a mag-fed rifle.
2.88+ coal is aggressive in AICS mags.
You referenced coal in mag against tight throat to bore. Post observance is also coal. O-give reference is only to 142SMK as a bullet without associated seating depth.

Not sure what you were expecting given the stated.

edited to add; your better off where it's at now.
That may be the case. I was just expecting to see a little shorter seating depth.
</div></div>

 

[hammerhead]

Re: .260 in aics mag. can you reach the rifling?

I would carefully check the length of the engraving on the bullet of the round you chambered. You may well have been engraving the bullet rather than pushing it back. That would account for the longer COAL than you expected.

 

[427Cobra]

Re: .260 in aics mag. can you reach the rifling?

My advice is is to order a 260 reamer with a .294 neck(not for Lapua brass) or a .297(Lapua braas) with no Freebore\Throat at all, and order a throating reamer so you can have your gunsmith set the the distance to the lands off your dummy round, my 260 started off with a 139 Scenar touching the lands with a Ojive measurement of 2.150, that is a COAL of about 2.750, now after 3300 rounds a 142 SMK is touching the lands with a Ojive of 2.235, COAL 2.850, I'm done with chasing the lands on this barrel, I'm going to shoot 142 SMKs until the barrel goes south.

 

[Ratbert]

Re: .260 in aics mag. can you reach the rifling?

How much neck tension did you have? If it was enough to seat it back and then stay in place when you extracted, most likely it was just jamming the bullet into the lands. Get a Hornady (Stoney Point) gauge and measure what the actual distance to just touch the lands.

I have a "standard" (no special instructions) PTG 260 reamer and had no problem touching the lands using 139 Scenars, not that I need to.

 

[Ratbert]

Re: .260 in aics mag. can you reach the rifling?

I don't know what you plan on doing with this gun and this is just my opinion, but I don't think it's a great idea to develop a load designed to touch the rifling for a gun used in practical long range matches or field use. Especially not to arbitrarily decide that that is your GOAL before you've ever even shot the thing or gathered any loading data and for a couple of reasons:

1) Our game is not generally played 15 yds from the parking lot with a rolling chest of tools at hand for any repairs or malfunctions that occur. You pack in what you need and the rifle had better be able to perform using whatever you brought or you're done for the day. Loading into the lands just takes one cartridge loaded a little too long with a little bit of a loose neck to pull apart when you go to extract between stages to stick the bullet and a dump a load of powder in your chamber. Sounds unlikely but I've seen it happen several times. I'd much rather be able to load a round into the chamber and not have to worry that if I don't shoot it the bullet will end up stuck in the barrel.

2) No seating die is ever going to provide absolute repeatability. There's always going to be cases that, due to variances in neck tension or jacket thickness or whatever end up seating a little bit longer or a little bit shorter. Not much, but if you are designed to be just touching the lands this will make the difference between just touching, jammed in, or just shy. If you're trying for precision then I wouldn't want it to be a crap shoot to know which of the three scenarios I'm shooting each time. If you design for 0.015" jump then 0.005" variance results in jumping, jumping, or jumping. Considerably more consistent circumstances. Alternatively you could soft-seat and jam it hard into the lands every time like the benchrest guys, but refer back to reason 1.

3) The throat on your 260 is going to move on you. Especially in the first 300-500 rounds. Go to a 3 day match shooting 180rds and you may start with a load that is just touching the lands but by the end of the 3rd day that's not going to be what you have any more.


Obviously some guns demand that a certain projectile be loaded in the lands. I tried every 6.5mm 130gr bullet I could find and the only way I could get them to shoot was to put them into the lands. And as the throat pulled back over time the gun started shooting like shit until I chased it down with a longer cartridge. I switched to a 139 Scenar, loaded it to a reasonable jump and it shot great with the same load for another 1200 rounds and I'm confident that if I were to screw the barrel back on and take it out today it would still shoot 1 hole groups.

 

[maccrazy2]

Re: .260 in aics mag. can you reach the rifling?

Thanks guys.
I do not plan on loading into the lands but it did want the option to be able to if i wanted to. I had heard about the amount of throat erosion on this round and am a little concerned about starting out with this much jump before any wear has happened.

 

[maccrazy2]

Re: .260 in aics mag. can you reach the rifling?

I spoke with dave this morning. I will get the throat numbers off of the reamer to verify they match the build sheet. It shows a throat legenth of.2195
it is set up for lapua brass at. 297 neck.
I will find out tomorrow after i get the reamer numbers.

 

[427Cobra]

Re: .260 in aics mag. can you reach the rifling?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: maccrazy2</div><div class="ubbcode-body">Thanks guys.
I do not plan on loading into the lands but it did want the option to be able to if i wanted to. I had heard about the amount of throat erosion on this round and am a little concerned about starting out with this much jump before any wear has happened.
</div></div>

I have 3300 rounds down my 260, its not 308 barrel life, but its also not 6.5-284 barrel life either.

 

[maccrazy2]

Re: .260 in aics mag. can you reach the rifling?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: maccrazy2</div><div class="ubbcode-body">I spoke with dave this morning. I will get the throat numbers off of the reamer to verify they match the build sheet. It shows a throat legenth of.2195
it is set up for lapua brass at. 297 neck.
I will find out tomorrow after i get the reamer numbers. </div></div>
Well i got home and checked and there is no throat legenth on the reamer. I guess it dosent matter at this point. I will just shoot it and see how it shoots.

 

[maccrazy2]

Re: .260 in aics mag. can you reach the rifling?

I dug out a cartridge gauge and bullet gauge
COAL with bullet lightly touching lands measures 2.945measured with 5 random 142smk's
base to ogive
2.385 using the .250 hole in the gauge
2.308 using the .260 hole
I do not have any other intermediate sizes to measure with on hand.

 

[maccrazy2]

Re: .260 in aics mag. can you reach the rifling?

So I got together with Dave and my gunsmith today and determined the reamer is not what I ordered. I am going to send in the reamer to be reground and shoot the gun and see how it groups. If it shoots well now I will run it untill accuracy falls off and then have the barrel set back and rechambered so I can chase the lands as needed. Dave is confident it will shoot well as is but .080 jump to start with is more then I want. The bullet has alot of bearing surface so it may shoot ok but I am just concerned about how it will be down the road after some throat erosion.