Tight neck in the rain

[noload]

Im running a half thou. neck clearance on each side. I shot today in the rain and got some high pressure signs. Do you think rain drops on the necks caused this? Making for a hard bullet release, Or due to the round being wet ?? I shot the same load the day before with no pressure signs. Temp was cooler the raining day. Load = 180 VLD, 56.4, 4831sc.

 

[jonbearman]

I always thought that .0015 was the bare minimum to .002 being the standard.

 

[markr]

If this is a target rifle with a custom chamber IMHO you are running too close on the tolerances anyway. Depending on caliber and chambering, any brass flow into the neck could cause serious pressure problems....quickly!
I recommend that you take a tubing micrometer to you necks and check each and every one in several spots around the neck, then measure the pressure ring on the bullets if there is one so that you will know the exact measurements to add up. As well, a chamber cast would be helpful so that you know the exact tolerances that you're looking for.
.002 to .003 is about the minimum clearance that you should be looking for and once again. it doesn't hurt to check neck thickness on the necks frequently if you are running close tolerances.

 

[Steve Blair]

In target rifles, I use .003-.004" for small calibers and .004-.005" for larger. Diametral clearance of .001" is too tight. My .284 Shehane F-Open rifle has .004" clearance, a Ø.313" chamber neck and Ø.309" loaded cartridge neck diameter. In hunting rifles, I run standard size chambers and unturned brass.

 

[spclark]

Shooting in the rain, with water on your cartridges when you load 'em, will always produce pressure signs not present with the same rounds fired dry.

Water does not compress (ask anyone who's ever sucked water into their vehicle's engine driving thru a flooded road) and also will tend to act as a lubricant so the forces acting on your bolt will be greater.

0.001" total neck clearance is fine in a benchrest rifle (more often than not but then they don't get shot in the rain much, do they?) while 0.003" - 0.004" is more a minimum for prone rifles, even more for gas guns.

 

[noload]

I think.... AFTER further Review, Betwix the wall clearance and the pressure bulge on the bullet, and the rain drops, all added up, was too much stuff in a small space. I did turn another .002 off the necks. Thanks for all the comments, It did confirm my thoughts.

 

[spclark]

It'll remain a problem if you shoot in the rain without taking some steps to keep water off rounds going into your chamber and into the chamber itself. Where shooting in the rain is a frequent practice, some folks fabricate rain shields for their rifles out of things like old propellant bottles that can quickly be attached with Velcro or rubber bands to cover the loading port.

Loading from a closed cartridge box is a PITA while covering one with a towel or something helps a great deal & allows the next round to be pulled much more easily. Keep another handy to dry your fingers too aids in ammo handling as well as bolt manipulation.

 

[TheBlueEyedBear]

I gleaned from reading many posts on this subject was that in the small BR cartridges that .001 to .003 was normal. But, as you went up in caliber the clearance would increase. This increase was due to the load size and its resulting pressure.
I believe this was mentioned in a recent post by Boyd Allen regarding Chamber design.

 

[Steve Blair]

I gleaned from reading many posts on this subject was that in the small BR cartridges that .001 to .003 was normal. But, as you went up in caliber the clearance would increase. This increase was due to the load size and its resulting pressure.
I believe this was mentioned in a recent post by Boyd Allen regarding Chamber design.

[br]
Boyd is a benchrest shooter and almost always speaks from that viewpoint. Although there is nothing wrong with that and his advice is well given, the requirements in other disciplines are very different.