I am giving serious thought to getting a Kimber Montana 280AI
I am curious as to how much velocity would be lost by shooting standard 280 ammo out of the 280AI Chamber and if there is any accuracy loss in doing so ?

Thanks

Not sure about velocity loss. Maybe 100fps? As to accuracy, it can be just as good as your worked up AI loads.

cant speak about velocity loss,as I had no way to test it,but as for accuracy,I found a load that would give excellent accuracy when fire forming 6mm to 244AI. interestingly,full power loads would usually split the neck,lower power wouldn't fill out the shoulder completely.
just right ,though,and I get fully formed brass,and sub moa shooting,at around 3000 fps,with 85 gr bullets.

My Kimber Montana 280ai does very well with factory loads, no comment on velocity.

my .223s lost ~100 fps with the same load after I had the chamber improved. accuracy did not suffer.

I've shot a 280AI for close to thirty years. During that time I've fireformed many factory loads. Generally I have not had much velocity loss from a standard 280 baseline velocity. One thing stands out though: factory loads being blown out have given me some of the most ungodly groups my AI's ever fired...bunch of little bitty bug holes! I don't know why, but it happens....I would hate to know my AI's prefer low velocity loads......dear God.

I have been shooting my Kimber 280AI with both AI and standard loads and I can attest to what has been already said. Some of the standard 280 loads have been very accurate in my rifle. Then I have the advantage of both an accurate load and a newly fire formed case.

In a couple of AI's fire forming loads often give exceptional accuracy.

The FF load Dober gave me for the 7mm Masburn does 3150 with a 139 Hornady,and in my rifle I can hunt with it just as it's set up. No re zero needed. It shoots very well also.

My experience is basically the same as everybody else's. There's always some velocity loss when shooting standard ammo in an improved chamber, but exactly how much depends on the powder, bullet, etc. I've owned rifles for several "improved" cartridges, but can't recall a loss of more than 100 fps.

Accuracy is usually good with fire-forming loads, but how good again depends on the load. If the bullets are seated crooked in fireforming loads, then they probably won't group very well, but if the loads are put together correctly then accuracy can be outstanding. My fire-forming loads in several rifles have been accurate enough to shoot ground squirrels and prairie dogs at 200-300 yards.

My 280, 22-250 and 257 ack groups forming loads almost as good as the formed loads. The last cases i formed for the 280 i used Unique and cream of wheat, but never took the time to group the cream a wheat on paper so can't say about that load.

This is a 280 AI fire forming session. 40 rounds as I recall.
I didn't worry too much about accuracy and group size, I just wanted the brass. The load was a 280 Rem Max load with a 154 gr Hornady Spire Point, the bullets were given to me.

JD338

JD
That is about what I got using the same bullet and 280 max loads using IMR 4350. I haven't loaded the 154 Hornady's in the improved case yet as I have too many others and the weather is no cooperating enough to go out yet.

I bought a bunch of 154's a couple of years back for $15 a box in a Mom and Pop store in shotgun country.

Thanks Guys
I appreciate the information

With full power 280AI loads, she is a shooter.
160 gr AB with RL22 .092" c/c.

JD338

Unless it is coincidence, I see more sub 1/4" groups from 280 A1 owners that very other cartridge pic's combined.

Am I wrong?

Yes.....

They just like to post a lot.

We can't help it if we like to brag! My best group with my 280 AI was .135 at 100 yards...eyes too old to do that again!

Factory .223 loads in my .223 AI lose about 75 fps but shoot as accurate as my AI handloads, easily varmint capable to 300 yds.

Godogs laffin! I did something like that too....with a 30/06.

I'm envious of you Montana varmint shooters :
Ground Squirrels at 200 lined up with Prairie Dogs at 300 !
Now That is Shootin ;-)

The 280AI is as fast as the 7 RUM, accurate as a 6mm PPC and easy on barrels as a 22 short.

My 375AI does not notice the difference between fireforming loads and full-on hunting loads. A number of folks here have shot their best groups ever with it. Many nudging a quarter-inch at 100 yards with any number of different loads.

A fireforming session some time back with several different factory loads and several varieties of handloads produced a group of just over an inch with about 50 shots and four shooters.

Pretty much agree on all points except barrel wear. I've shot a lot of deer with one of mine and had to replace the barrel 3 times in the process. The first barrel was a Hart manufacture and it lost its mojo at about 600-700 rounds. Other manufacturers barrels lasted much longer though.