HEAD0001

I ordered an MGM barrel for my Encore. I asked the smith to cut a tight chamber. He asked me what measurement I wanted. So here goes. I sized the neck of my brass with a .264 Sinclair neck mandrel. I am using Lapua brass. It is very consistent in size. Before sizing the ID was .258, the OD was .289. After sizing the ID was .262, the OD was .292. The smith recommended cutting the chamber to .290. Does that sound right to you guys??? I have not given him these measurements yet. He did ask for them. He also asked for a dummy round. I would like to shoot the Nosler 120 gr. BT bullet. The problem is that I am not sure how to do a dummy round. I always did mine after I got the rifle, not before??? I will be using a Redding bushing sizing die. I selected the .263. Tom.

6.5 x 284 Cartridge

bigcountry

I would go for .001" over a round that you seated a bullet in. Not just sized.You can always turn the necks. But his measements are tight. Lapura usually have some thick necks however.

HEAD0001

It is my understanding that Lapua brass is very tough stuff. Or should I say made to last. It is also very consistent. The neck thickness, and diameter's are very consistent. I measured a dozen, they were all within .001 Tom.

bigcountry

They better be, have to morgage my house for some.

eldeguello

NO! It sounds too tight, unless you plan to turn those necks down. When you seat a .264" bullet, if the ID is .262" before you put the bullet in, your neck will have an O.D. of .294" after seating thebullet. This is.004" TOO BIG AROUNDfor a .290" diameter chamber neck.

I am pretty certainthat with such measurements, you cannot count on the bulletbeing easily released from the case mouth.ThisCOULD result in quite excessive pressures. It is essential for the bullet to FREELY ESCAPE the grip of the case mouth whenfired!

When you take a fired case out of that rifle, a new bulletMUST FREELY DROP through the mouth into the case to work safely. I would want a minimum clearance between the case neck diameter and the chamber neck of at least .002"-.003". You don't want accuracy and close tolerances at the expense of safety in such a hot round as the 6.5-.284!

If you cut the chamber neck to .290", and then turned the O.D. of your cases down to .289" with a bullet seated, it might workOK as long as the case necks don't come out too thin after turning them....

Good luck!

HEAD0001

The necks on the brass are extremely consistent(I have 500 casings), so I do not want to turn them(no need to). I am trying to determine what to cut the chamber at. I am pretty sure the smith will know-when I send him the measurements. I am also goint to do what Bigcountry said to do. I am going to seat a couple, and watch for further expansion of the neck.

My goal was to not seem like a complete idiot when I discussed this with my smith. Thanks, Tom.

Roskoe

I have built a bunch of 6.5-284's with both standard necks and tight necks. The standard neck is .299 on my reamer -loaded rounds are about .005 smaller.My tight neck reamer runs .294 - and requires a littleoutside neck turning. Some folks I know are running necks as tight as .290 for thousand yard shooting.

ShatoDavis

Once again Roskoe has come through!

.290 is way to tight, you would have to turn way too much material off. If you don't want to turn your necks I wouldn't go any tighter than .294 and you may have to turn some then. I'm guessing here but I imagine your OD will be close to .294 when you seat a bullet in your case. If so, you will need a .296 minimum IMHO considering that you don't want to neck turn. Let me ask this, If you don't intend to neck turn why are you ordering a custom reamer, with a tight neck? The two are generally not mutually exclusive.

Making a Dummy round is simple. Just measure your bullet. then seat the bullet in the sized case with no primer or powder. Then use your caliper to determine where the base of the bullet is. (open caliper to the length of the bullet, then hold one side at the tip of bullet and look to see where the lower jaw is in relation to the case) You want the base to be approximately at the neck/ shoulder junction. You don't want the base up in the neck and you don't want it intruding into the powder capacity either. This round will be very helpfull for your smith to order a custom reamer. But, I say again, I'm not certain you need a custom reamer. Why not just ream with a standar .299 reamer. Is the approx .002 worth it to you? I don't think you are going to realize any benefit, especially considering the platform. Trust me a standard neck will do quite sufficiently IMHO

Roskoe

As far as minimum neck wall thickness goes,my 6MM PPC benchrest reamer cuts a .262 neck. I prepare my cases so the loaded rounds measure .261. With a .243 bullet, that puts the neck wall thickness at .009. These are pretty thin. Probably about the lower limit of whatis practical.

I personally like to see ahuntingrifle set up so the neck is cut .005 bigger than the neck diameter of a loaded round. If you are not outside neck turning, the natural variations in neck wall thickness are generally going to dictate at least that much clearance for reliability. And, of course,require you to pay attention to different brands and lots of brass. A neck clearance issue will send pressures through the roof.

If you built a 6.5-284 with a neck wall thickness of .009, the neck of a loaded round would measure .282. That's a lot of trimming!

ShatoDavis

Roscoe has given Excellent advice from a very knowlegable man you would do well to head his advice.

Rokoe, if you wouldn't mind, would you look up my thread on bullet selection. I would be interested in getting your take. Thank you