I recently ordered a new box of .308 168 TTSXs. About a month ago, my previous accurate MOA load for my .300 WSM inexplicably produced a ~2"" group - way off from my expected group size. I assumed that perhaps throat erosion could be the culprit and so I attempted to re-measure my distance to the lands with this bullet.
To my surprise, I found that about half of the remaining 168 grain TTSXs from my new box would not fit into my Hornaday .300 WSM modified case - the first time this happened (I've been using this bullet since 2013). I measured the bullet diameters with my calipers and found different (granted, this is not a very accurate measurement approach, but it was my only option).
I sent an email to Barnes asking if their was any reported issues to this lot of bullets - I've pasted their response at the end of my post - at least the relevant part of their, that is.
This is fine, but the fact that 1/2 of my bullets would not properly slide into my Hornady Modified case indicates that the bullets in my new box of 168 TTSXs had slightly different diameters, which in turn would presumably result in different pressures (i.e., explain my enlarged group).
For the bullets that did fit into my modified case, my throat measurements did not changes since the last time I measured.
All this to say is that at least for me, If I ran into pressure problems, slight/qualitatively different differences in bullet diameter could be the cultprit.
"To get a precise measurement on the diameter it is best to use a micrometer and not a set of calipers. A ten thousandth of an inch (.0001”) #or .0002 to .0005” is a very precise measurement and you can easily get that by just the pressure with your hands using a set of calipers. A monolithic bullet such as a Barnes TTSX is made out of solid copper wire that has a preset diameter. You may see one at .3082” but not .3085”. It is impossible for a solid copper bullet in 30 caliber to pass through our dies during manufacture if they are over .30820” let alone .30850”. If you are reading .30850” that would be in the variance of your calipers. If you read the specs for your calipers you will find they allow for a tolerance variance of so many thou during the manufacture of those calipers. Calipers have to be calibrated as well with a proper gauge very often to be accurate. But even at that they vary. We only use calipers for quick length measurements. For measuring bullet diameters we have very high end micrometers that are extremely accurate.#In the bullet world, a monolithic bullet is by far the most consistent construction for diameter. A jacketed lead core bullet will have much greater variations throughout a run/lot.#But to answer your question, a 30 caliber or .308” diameter bullet has a SAAMI (Sporting Arms and Ammunition Manufacturers Institute) spec that allows a diameter of anywhere between .3070” to .3090”. A bullet of any of those sizes will fire and shoot just fine in a .308” diameter rifled barrel without issue. You would see MUCH greater increase in velocity or pressure just by changing a powder lot number primer brand then you would see in .0002” of diameter change in a bullet. So no, you will not receive a higher pressure if a bullet diameter increases by .0003”.#And also no we have not heard of a diameter issue on those bullets. As mentioned we don’t receive diameter issues on any of our monolithic bullets. Its just in the nature of how they are built. Our jacketed bullets however require very close inspection during manufacture to keep a consistent diameter. The diameter of the lead cores can change from one core to the next, or the strip thickness on the jacket can change. Other causes as well.#If you slightly chamfer the inside of the case mouth on your modified case it will help with the bullets sliding in easier. Same when seating the bullets.#Hope this helps. If you have anymore questions let me know! #Thank You,#Chase Young#| Consumer Technical Support |
Barnes Bullets"
To my surprise, I found that about half of the remaining 168 grain TTSXs from my new box would not fit into my Hornaday .300 WSM modified case - the first time this happened (I've been using this bullet since 2013). I measured the bullet diameters with my calipers and found different (granted, this is not a very accurate measurement approach, but it was my only option).
I sent an email to Barnes asking if their was any reported issues to this lot of bullets - I've pasted their response at the end of my post - at least the relevant part of their, that is.
This is fine, but the fact that 1/2 of my bullets would not properly slide into my Hornady Modified case indicates that the bullets in my new box of 168 TTSXs had slightly different diameters, which in turn would presumably result in different pressures (i.e., explain my enlarged group).
For the bullets that did fit into my modified case, my throat measurements did not changes since the last time I measured.
All this to say is that at least for me, If I ran into pressure problems, slight/qualitatively different differences in bullet diameter could be the cultprit.
"To get a precise measurement on the diameter it is best to use a micrometer and not a set of calipers. A ten thousandth of an inch (.0001”) #or .0002 to .0005” is a very precise measurement and you can easily get that by just the pressure with your hands using a set of calipers. A monolithic bullet such as a Barnes TTSX is made out of solid copper wire that has a preset diameter. You may see one at .3082” but not .3085”. It is impossible for a solid copper bullet in 30 caliber to pass through our dies during manufacture if they are over .30820” let alone .30850”. If you are reading .30850” that would be in the variance of your calipers. If you read the specs for your calipers you will find they allow for a tolerance variance of so many thou during the manufacture of those calipers. Calipers have to be calibrated as well with a proper gauge very often to be accurate. But even at that they vary. We only use calipers for quick length measurements. For measuring bullet diameters we have very high end micrometers that are extremely accurate.#In the bullet world, a monolithic bullet is by far the most consistent construction for diameter. A jacketed lead core bullet will have much greater variations throughout a run/lot.#But to answer your question, a 30 caliber or .308” diameter bullet has a SAAMI (Sporting Arms and Ammunition Manufacturers Institute) spec that allows a diameter of anywhere between .3070” to .3090”. A bullet of any of those sizes will fire and shoot just fine in a .308” diameter rifled barrel without issue. You would see MUCH greater increase in velocity or pressure just by changing a powder lot number primer brand then you would see in .0002” of diameter change in a bullet. So no, you will not receive a higher pressure if a bullet diameter increases by .0003”.#And also no we have not heard of a diameter issue on those bullets. As mentioned we don’t receive diameter issues on any of our monolithic bullets. Its just in the nature of how they are built. Our jacketed bullets however require very close inspection during manufacture to keep a consistent diameter. The diameter of the lead cores can change from one core to the next, or the strip thickness on the jacket can change. Other causes as well.#If you slightly chamfer the inside of the case mouth on your modified case it will help with the bullets sliding in easier. Same when seating the bullets.#Hope this helps. If you have anymore questions let me know! #Thank You,#Chase Young#| Consumer Technical Support |
Barnes Bullets"
