Out of spec. 458 Lott chamber causing problems

[Pirkan]

I´ll start this thread by prefacing that this rifle is my first big bore and it´s my first time reloading a straight-walled caliber. The rifle is a Brno 602 rechambered to 458 Lott from a 458 Win Mag.

I recently made some very weak handloads (400 gr @ 500 ms) with cheap H&N bullets and N32C powder. Beacause of them being so weak i did not bother crimping them but I later noticed that they would not chamber despite the brass being trimmed to 71 mm, CIP max is 71.12 mm. The bullet did not show any signs of being the cause of this however the case mouth showed signs of contact which should not happen. This has lead me to the conclusion that the chamber was cut a bit to short, CIP min is 71.37 mm. The worst part about this is that I have already shot about 30 rounds of full power ammo, both factory (Hornady Dangerous Game Series) and hand loaded that was crimped and did chamber because of the decreased diameter near the case mouth. The spent cases from both the Hornady and the hand loads show some thin pieces of brass protruding from the case mouth which I worry might cause increases in pressure because this means that there is a layer of brass that might act as a minor obstruction for the bullet initially. I have not noticed any signs of high pressure yet but I want to be careful. Some cases do not show this little lip but all fired cases are 70.7 mm long without the lip. This means that the chamber is 0.67 mm to short.

I was hoping to hear from people that are more knowledgeble than me on this subject regarding if this is dangerous or not. In the meantime I will not shoot the rifle and try to contact the smith who did the work.

I apologize for any lingustical errors because English is not my first language.

The first picture shows spent cases from factory ammo and the second picture shows cases from my hand loads. The last picture is the CIP dimensions.

 

[Inline6]

Talk to your smith, the round will head space off the ring at the base of the cartridge. If he sinks the reamer in more to clean up the depth of the case it can/will affect your head space.

I wonder how new/old the reamer is?

 

[IvW]

I wonder how new/old the smith is?......

 

[Pirkan]

I've contacted the smith and will wait for his response before I talk to bad about him but I thank you all for your input.

 

[SRvet]

Doing a chamber cast might be useful, sounds like his reamer is out of spec or he didn’t ream deeply enough

 

[Inline6]

Doing a chamber cast might be useful, sounds like his reamer is out of spec or he didn’t ream deeply enough

It head spaces off the belt. If it was not deep enough the bolt would not close. OP can check that pretty fast with a piece of scotch tape on the back side of the case. Put a piece on the case head and trim with a razor or sharp knife around the rim so you do not have any extra overhanging (keep adding layers until you feel resistants, should be on layer 2 or 3). His action could have a little extra play in it, smith set up the head space correct but the depth of the case is not deep enough. As in the action has more room than needed. It chambered on a live round so it was an easy oversight by the smith (if that's what happened).

 

[86thecat]

There are reamers designed to rechamber a Win Mag to Lott which will not cut the belt area deeper. If your smith used a standard Lott chamber reamer he may have cut the chamber a little shallow trying not to cut the belt area deeper and create excess headspace. It is easier to control the reamer depth with barrel in a lathe but tough to control depth if barrel is still on rifle and reaming by hand.
Hopefully no damage to your rifle but wouldn't be a bad idea to have it checked for bolt lug setback.
Definitely have the chamber cut to proper depth before shooting again.