Custom reamer and dummy round....need advice.

[Colin78]

I'm building a 6.5 saum gap 4s and my smith said to load a dummy round, send it to him and he is going to have a custom reamer made. But I have questions I hope you can help me work thru.

I'm wanting to shoot the 129 Accubond LR and 142 Accubond LR. I like loading my ammo where a lot of bullet is sticking out of the case (sexy looking imo, and doesn't take up powder capacity). so I took the shorter of the 2 bullets (129 gr) and seated them where I have 1 bullet diameter of bearing surface in the case neck (.264) there is more bullet in the case due to boat tail. The standard reamer for the gap 4s is .120. When I measure my dummy round and compare it to how it would fit in the standard.120 freebore I'm coming up that my custom reamer is going to be like .220. That would be bullet to lands. Kinda scares me that it is so different. Now I should have mentioned I'm building off a long action so I'm not worried about COAL and fitting in a little magazine. And my experience with the Accubond LR bullets like a ton of jump so I'm thinking even though my dummy round is one thing when I get the rifle and start to work on load development I'm going to be seating the bullets a good bit further in the case.

Is it unusual to have a custom reamer with that much more freebore than standard? Am I looking at this all wrong? Do you have any suggestions?

 

[elkaholic]

Thats not at all unusual and can increase performance when you have the room. Where trouble sometimes comes is when switching bullets, so I would give some thought to that depending on what else you might want to shoot. That said, .220 FB sounds like you are on the right track although I dont know personally just what the LRAB needs?

 

[Colin78]

Thanks for the reply. And yes that is part of my delima. Primarily I want to shoot the lighter bullets as fast as I can and get them to be super flat for deer sized game but that's not to say I might not want to play around with the heavies for some long range targets. I'm thinking if I throat it as long as possible and still be good with the lighter bullets I'll still be good for the longer heavies.

 

[Edd]

Based on the Nosler data, the 142 gr bullet is .100" longer than the 129 gr bullet. So, if you load them to the same OAL, you will have .100" more bullet in the case with the 142 gr bullet. On a .264" diameter bullet, .100" of length occupies about 1.375 grains of space. Depending on the powders used, the powder charge used for a 142 gr bullet could very likely be 1.375 gr less.

 

[Colin78]

Based on the Nosler data, the 142 gr bullet is .100" longer than the 129 gr bullet. So, if you load them to the same OAL, you will have .100" more bullet in the case with the 142 gr bullet. On a .264" diameter bullet, .100" of length occupies about 1.375 grains of space. Depending on the powders used, the powder charge used for a 142 gr bullet could very likely be 1.375 gr less.

Yes sir. And that is what kinda baffles me about this. I'm looking at having my freebore .100 more than the standard long freebore for the gap 6.5 saum. So I'm thinking if everyone else is getting such good velocity out of that .120 freebore I should be that much ahead with a .220 freebore. Heck a lot of guys are still using the .081 freebore. Those bullets would really be crammed down in the case taking up a ton of powder volume.

 

[Edd]

They are using bullets with a short bearing surface. Measure the length of the full diameter part of your Nosler bullets and compare that to the bearing surface length on the Berger spec sheet.