Long Bullets / Short Throat

Chinbullco

Chinbullco

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Trying to find an answer to a nagging question. This is an experimental / mental project. Will a long bullet in a quick twist barrel, with bullet base seated below neck and close to lands cause high pressure spikes? Is it possible for bullet obturation to begin before bullet leaves the cartridge? First few loads worked fine, as cartridges were loaded and reloaded more lift was required to open bolt. Did work hardened brass contribute to higher pressures? The cartridge is a 6.5 WSM, barrel is 1:7 twist, bullet 170 gr. ultra low drag. Retumbo from same lot used through-out testing. Case neck clearance in chamber 0.010".
 
Primary extraction happens on bolt lift when the case is moved slightly to the rear. This is controlled by camming action within the bolt and the camming action depends on how the bolt is designed. Lubing the camming surfaces reduces bolt lift with any good grease.

Second, you have a short bodied cartridge case with not much surface area to grip the chamber walls. This increases bolt thrust and can cause hard extraction. If you are neck sizing then try full length resizing these cases and bump the shoulder of the case further back and create more head gap clearance or "air space" between the rear of the case and the bolt face.

Many of the cases I fire form are jammed hard into the rifling and loaded with a mid range load and I have no problems with pressure spikes, hard bolt opening or pressure signs on the cases.

You have a primary extraction problem, and you need to find out "why".

1. What type bolt action do you have, if it is a Savage rifle there is a simple fix.
 
Chinbullco said:
Trying to find an answer to a nagging question. This is an experimental / mental project. Will a long bullet in a quick twist barrel, with bullet base seated below neck and close to lands cause high pressure spikes? Is it possible for bullet obturation to begin before bullet leaves the cartridge? First few loads worked fine, as cartridges were loaded and reloaded more lift was required to open bolt. Did work hardened brass contribute to higher pressures? The cartridge is a 6.5 WSM, barrel is 1:7 twist, bullet 170 gr. ultra low drag. Retumbo from same lot used through-out testing. Case neck clearance in chamber 0.010".
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Interesting since first few loads worked fine.

The short throat in my old 264 WM was a real pain as I had to load 140gr. bullets fairly short and had to intrude on powder space. One load was fine and once blew a primer by adding .5 grains working up. Maybe its just Retumbo behaving that way, I would try another powder just for the hell of it (before reaming the throat)
 
Pathfinder said:
Interesting since first few loads worked fine.

The short throat in my old 264 WM was a real pain as I had to load 140gr. bullets fairly short and had to intrude on powder space. One load was fine and once blew a primer by adding .5 grains working up. Maybe its just Retumbo behaving that way, I would try another powder just for the hell of it (before reaming the throat)
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I tried H1000, R22, R25, IMR 7828, IMR 4831, and not yet US 869. I am starting with light loads and going no further as pressures extrude case. I am thinking the bullet obturation is taking place before bullet clears neck. Looked through a pile of loading manuals looking for reference to incidents where this may of happened but haven't found anything. It shoots 140's fine.
 
re Long Bullets/ Short Throat

Linda Lovelace may have experienced a similar throat incompatibility problem in a somewhat different field, Sorry Dale;)
 
Crystal chandelier in the outhouse???

Chinbullco said:
Not a Savage fan. Building a custom rifle on a Savage is like hanging a crystal chandelier in the outhouse. RPA Quadlock receiver.
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Hi Dale, During our phone call last night we discussed everything but this problem....RPA Quadlock. This was designed mostly for .308. It has 4 lugs and all extraction in 45 degs or less of bolt lift. You are extracting a monster fat case and pretty straight too, and driving the longest heaviest 6.5 bullet I've ever seen. Maybe using a Savage action with 2 lugs might not be the "outhouse" you think it is. BTW I built 2 custom rifles on Stevens 200's, one short and one long. The long action is now a 30/8X68 impvd. They work just fine ....as long as I stay up wind, and the chandlier doesn't blind me. :p

NormB
 
I have a 6.5x55 that is specifically throated for 120-125 grain bullets. [Shilen 1-8" twist]
If I seat a 140-142, it sits pretty deep in the case to clear the rifling at the throat.
I am sure it is obturating the bullet before it is clear of the neck.

But I have experienced no issues when doing this....accuracy and pressures seem fine.
Velocity is close to what I would expect with the 6.5x55 and the bullets in the 140 grain class.

It is very accurate with anything I have so far shot from it.

Regards, Eagleye
 
NormB said:
Hi Dale, During our phone call last night we discussed everything but this problem....RPA Quadlock. This was designed mostly for .308. It has 4 lugs and all extraction in 45 degs or less of bolt lift. You are extracting a monster fat case and pretty straight too, and driving the longest heaviest 6.5 bullet I've ever seen. Maybe using a Savage action with 2 lugs might not be the "outhouse" you think it is. BTW I built 2 custom rifles on Stevens 200's, one short and one long. The long action is now a 30/8X68 impvd. They work just fine ....as long as I stay up wind, and the chandlier doesn't blind me. :p

NormB
Click to expand...

New RPA Quadlocks are now available with magnum bolt face.
 
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