Cooper Rifles and Max Loads

[deertroy1]

Any of you Cooper rifle owners having difficulty reaching maximum loads? I just got a new to me Cooper in 6mm Rem and it will not reach anywhere near what my other 6mm rem will achieve even though it has a 2" longer barrel. I thought it may be a carbon ring but after a thorough cleaning and verification with a borescope it still won't accept anything near max.
My gunsmith said Coopers can be notorious for that as they have a small barrel tenon vs other brands. I read a little about this phenomenon here!

 

[DJ Fergus]

I know a larger tenon will handle more pressure but I assume you won't know the difference until the barrel has enough repeated extreme pressure loads to fatigue the barrel enough to fail. I could be wrong, this is just an assumption.

 

[JMW67]

not understanding what the tenon size has to do with this

 

[DJ Fergus]

It's hard for me to understand that the smaller tenon would keep velocity lower than average before reaching max pressure with all other things being equal. Maybe I'm wrong but it just doesn't seem likely.

 

[deertroy1]

Guy's I don't claim to know squat which is why I ask if Cooper owners are noticing difficulty reaching max loads and/or velocities?

 

[dls guide]

Maybe tight match chambers. I get top velocity with my two model 52's with less than book max loads.

 

[DJ Fergus]

Guy's I don't claim to know squat which is why I ask if Cooper owners are noticing difficulty reaching max loads and/or velocities

Yes, a tight chamber will reach max pressure sooner than a looser chamber.
I wasn't arguing with you about the tenon. I just thought it was unlikely. I've been wrong before though.

 

[JMW67]

Any of you Cooper rifle owners having difficulty reaching maximum loads? I just got a new to me Cooper in 6mm Rem and it will not reach anywhere near what my other 6mm rem will achieve even though it has a 2" longer barrel. I thought it may be a carbon ring but after a thorough cleaning and verification with a borescope it still won't accept anything near max.
My gunsmith said Coopers can be notorious for that as they have a small barrel tenon vs other brands. I read a little about this phenomenon here!

have you ran your loads with a chronograph or are just finding pressure before you thought you should going by charge weight

 

[dls guide]

What did the guys at Cooper say? I would talk to the builders first. Why don't you give some examples of this gun vs. your old gun.

 

[MtnTrax]

I have owned several Cooper rifles and have ever had an issue with velocity or accuracy

 

[Hunterjones]

I have owned 7-8 Coopers and loaded for another 3-4 and have noticed that chambers seem to be on the tight side with all of them but have never had a problem achieving max velocity safely with any given bullet. I have not really noticed excessive pressure and velocity when working up to max powder charges either.....
I DO have a Forbes 30-60 that reaches max velocity with 2-3 different bullets at 2-4 grains less than book max charges

 

[deertroy1]

That's the thing. I can't reach max velocity. I get max pressure nut velocity is lagging 200 - 300 fps?
Yes, the loads were chronographed with an Oehler 35
24" Cooper 70gr Sierra 3450fps Max
22" Savage (McGowen) 3750fps Max

Same brass, primers and powder. Bothe rifles headspace within 0.001" according to fired cases. Savage has a bit more leade but bullet seated nowhere near lands in either rifle.

 

[Hunterjones]

Hmmm....does the Cooper have a tighter twist?

 

[Mikecr]

How do you know that you have max pressure?
Less barrel steel around a chamber (smaller tenon) can lead to early popping extraction, but does not change load pressure.
This is an example of an often declared pressure problem, that is not caused by pressure.