40. cal bullet diameter question

[Bmac1949]

I'm getting ready to reload .40cal for a Sig P250. I will be using jacketed bullets. Midway list .40" and .401" in their .40 cal selection. I'm assuming that I will use the .40" bullet for the sig. If my assumption is right do I need to slug the barrel before I order bullets. The gun isn't in yet and I'd like to have my supplies together before it gets here. Thanks ahead of time.

 

[rcmodel]

.400" is the standard .40 S&W Jacketed bullet dia.

Some Plated and all cast or swaged lead bullets will be .401".

Either is fine, and there is no need to slug the barrel.

rc

 

[Bmac1949]

Thanks, just making sure.

 

[noylj]

Just for your information--it won't affect what you find you use in practice:
A diameter of a jacketed bullet should be the same as your barrel's groove diameter. A lead (cast or swaged) and plated bullet should be AT LEAST 0.001" larger than your barrel's groove diameter.
The good news is that jacketed bullets still perform fine even if they are slightly smaller than your groove diameter.
Your .40 S&W barrel could have a groove diameter of 0.401". In this case, standard jacketed bullets at 0.400" will still perform fine, but a lead or plated bullet of 0.401" may suffer gas-cutting and NOT perform well.
You can, provided you start with an appropriate starting load, use jacketed bullets that are as much as 0.002" larger than your groove diameter. However, your max load may be less than indicated in the reloading data source.
The first response when asked "can I use this bullet?" is "what is your barrel's groove diameter?"

 

[Bmac1949]

Good information I appreciate it.