Calculating Trim Length

[savagedasher]

Probably because they paid attention to my post on it. Thanks for the plug. It's slightly more accurate if you use a 22 WMR case and square off the rim as I did. (See photos above.) The 22 LR case works best for 22-cal chambers.

Thank for the compliment. but I have ben using it for years. I have a shot gun shell like chamber I use a shot gun for fire forming. using a 22 case. Larry

 

[CH Luke]

My .02, this is strictly a clearance issue....no "right" number other than making sure you have enough clearance for safety and all the necks are the same. Just listened to Jack Neary talk about it, he said he was using .035" and did not give the exact number much thought, BUT he did make sure all the necks were trimmed identical.

PS. if you care what Jack thinks, .010" or less clearance is "bad juju."

Sounds convincing. What I had read on another post here was .010 would help prevent a carbon ring build-up. Is it possible this is also true and the real key to what Jack is saying is that consistent brass length is the key, albeit stay with a bit more than .010"?

 

[Brians356]

Sounds convincing. What I had read on another post here was .010 would help prevent a carbon ring build-up. Is it possible this is also true and the real key to what Jack is saying is that consistent brass length is the key, albeit stay with a bit more than .010"?

No way. There's no magic to a .010" vs .020" or any other size gap WRT carbon buildup. Ain't buying that.

The first rule (for safety) is to make damn sure the cases never run into the end of the chamber neck, which if there is at least .010" margin is unlikely given the way most here monitor and minimally resize our cases. The second rule (for accuracy) is to trim cases the same length. There is no rule for carbon buildup WRT case lengths, that is strictly a cleaning issue, and possibly also a powder choice / charge issue.

 

[Brians356]

Thank for the compliment. but I have ben using it for years. I have a shot gun shell like chamber I use a shot gun for fire forming. using a 22 case. Larry

It matters the diameter and shape of the rim on the rimfire case in the Hornady tool. Sinclair's slug for 6mm is .2672" diameter and sharp-edged, which will actually go past the end of the neck proper and stop against the short 45-deg transition to the leade, somewhere in the middle of that ramp. Since most 6mm chamber necks (SAAMI) are ~.277", the Sinclair registers about .010" longer than the actual length. I turned my 22 WMR case rim to .275" diameter, and squared off, so that it catches at the outer edge of the transition. This setup indicates a chamber length .009" shorter than the Sinclair in my OEM Rem 700 in 6mm Rem. It's not much, but when people here are discussing letting their brass get to within .010" of the end of the chamber, it's significant.

 

[savagedasher]

No way. There's no magic to a .010" vs .020" or any other size gap WRT carbon buildup. Ain't buying that.

The first rule (for safety) is to make damn sure the cases never run into the end of the chamber neck, which if there is at least .010" margin is unlikely given the way most here monitor and minimally resize our cases. The second rule (for accuracy) is to trim cases the same length. There is no rule for carbon buildup WRT case lengths, that is strictly a cleaning issue, and possibly also a powder choice / charge issue.

The least amount of clearance You have the less chance of the carbon ring starting. Every one has that choice . Larry

 

[fguffey]

I believe a reloader should know the length of the chamber from the beginning of the throat to the bolt face. I believe it is a bad habit to trim cases to book length without knowing the length of the chamber. I see nothing wrong with being able to determine the length of the chamber.

I want to cover the entire chamber with my cases. Again, there are times it is not possible. Then there are RCBS ‘X’ dies, straight off at the beginning the instructions recommend trimming the case .020”. After that comes the confusion, some believe the ‘X’ die prevents case length growth. Others believe by the time the case grows and requires trimming it is time to start on another case.

F. Guffey

 

[savagedasher]

It matters the diameter and shape of the rim on the rimfire case in the Hornady tool. Sinclair's slug for 6mm is .2672" diameter and sharp-edged, which will actually go past the end of the neck proper and stop against the short 45-deg transition to the leade, somewhere in the middle of that ramp. Since most 6mm chamber necks (SAAMI) are ~.277", the Sinclair registers about .010" longer than the actual length. I turned my 22 WMR case rim to .275" diameter, and squared off, so that it catches at the outer edge of the transition. This setup indicates a chamber length .009" shorter than the Sinclair in my OEM Rem 700 in 6mm Rem. It's not much, but when people here are discussing letting their brass get to within .010" of the end of the chamber, it's significant.

When you get the number it will never change if the Same tool is used every time . You zero your caliper insert the tools . If the number is 1.552 3 weeks later The number is 1. 548 you know you have
.005 carbon ring . Do you trim the case
Or remove the carbon ring . In my case I remove the carbon ring . Better yet clean you gun so you don't have it . Larry

 

[NorCalMikie]

If you pick up a "new to you" rifle, you probably won't know any chamber measurements and more than likely, also won't have a reamer print.
How do you come up with the chamber length? Guess and hope you're right? MEASURE IT!! Write those specs down and refer to them before you do any trimming.

 

[savagedasher]

If you pick up a "new to you" rifle, you probably won't know any chamber measurements and more than likely, also won't have a reamer print.
How do you come up with the chamber length? Guess and hope you're right? MEASURE IT!! Write those specs down and refer to them before you do any trimming.

I wouldn't buy one without knowing . If I did I would core safe it. Larry

 

[NorCalMikie]

I wouldn't buy one without knowing??? You and how many other Guys think that way?? My guess is "not that many". If you buy a new rig, unless it's a custom build, it doesn't come with chamber specs OR a reamer print.
And the average Joe (in this case Larry ) isn't interested that much about the chamber specs. It was bought to shoot. As time goes by, that interest may change.
My point is, it's pretty easy to measure what you've got in front of you so you know what to expect. EVERY ONE of my rigs has been measured with the proper tools and that measurement written down and referred to when it comes to trimming (if needed) and loading. And, if the proper type dies are used, trimming will stay at a minimum or not needed at all.